Hot-dip galvanized steel sheet

ABSTRACT

A hot-dip galvanized steel sheet wherein the hot-dip galvanized steel sheet comprises a base steel sheet and a hot-dip galvanized layer, a ferrite phase is, by volume fraction, 40% or more and 97% or less in a range of ⅛ thickness to ⅜ thickness centered at a position of ¼ thickness from the surface of the base steel sheet, a hard structure is 3% or more in total, wherein the hot-dip galvanized steel sheet has the hot-dip galvanized layer in which Fe is 5.0% or less and Al is 1.0% or less, and columnar grains formed of a ζ phase is 20% or more in an entire interface between the plated layer and the base steel sheet on the surface of the base steel sheet in which a ratio of a volume fraction of the hard structure in a surface layer range of 20 μm depth in a steel sheet direction from an interface between the hot-dip galvanized layer and the base steel sheet is 0.10 times or more to 0.90 times or less of a volume fraction of the hard structure in the range of ⅛ thickness to ⅜ thickness, and wherein the hot-dip galvanized steel sheet has a refined layer at the side of the interface in the base steel sheet, and wherein an average thickness of the refined layer, an average grain size of ferrite in the refined layer and a maximum size of the oxide included in the refined layer are defined respectively.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a hot-dip galvanized steel sheet. Thepresent invention relates to a high strength hot-dip galvanized steelsheet particularly excellent in ductility, bendability, holeexpansibility, and plating adhesion at the time of bending deformationand excellent in cyclic bending fatigue resistance.

Priority is claimed on Japanese Patent Application No. 2014-225612,filed on Nov. 5, 2014, the content of which is incorporated herein byreference.

RELATED ART

There has been an increasing demand for high-strengthening of steelsheets mainly used for automotive frame members in recent years. Forthese high strength steel sheets, it is necessary to have formabilitiessuch as ductility, bendability and flange formability in order to obtaincomplex member shapes. In addition, since these high strength steelsheets are always affected by vibration when used for automotivemembers, it is required to have high fatigue resistance. Further, sincean automotive steel sheet is generally used outdoors, it is usuallyrequired for the steel sheet to have excellent corrosion resistance.

In uses for automotive outside sheets and the like, the peripheral partof a sheet is usually subjected to severe bending (hem bending) by pressworking. Not only in uses for the automotive outside sheets but also inother uses, a sheet is subjected to severe bending by press working,hole expansion working, or the like to be used in many cases. In thecase of subjecting a conventional hot-dip galvanized steel sheet tosevere bending, hole expansion working, or the like, the plated layer issometimes peeled off from the base steel sheet in the worked part. Whenthe plated layer is peeled off from the base steel sheet as describedabove, there is a problem that the corrosion resistance of the peeledpart is lost and the base steel sheet is corroded and rusted at an earlystage. In addition, even when the plated layer is not peeled off, theadhesion between the plated layer and the base steel sheet is lost, evensmall voids are formed in the area in which the adhesion is lost tocause external air or moisture to enter the voids. Thus, a function ofcorrosion resistance by the plated layer is lost, and as a result, asdescribed above, corrosion and rusting occurs in the base steel sheet atan early stage.

In view of such problems, for a high strength steel sheet for uses inwhich such severe bending or the like is performed, there has been astrong desire for developing a plated steel sheet including a hot-dipgalvanized layer excellent in adhesion of the plated layer with the basesteel sheet.

In order to enhance the adhesion of a plated layer, for example, asrepresented by Patent Documents 1 to 3, methods of forming oxides insidea steel sheet and reducing the amount of oxides at an interface betweenthe base steel and a plated layer that causes plating peeling areproposed. However, in such a case of forming an oxide on the surface ofthe steel sheet, carbon in the surface of the steel sheet is bound tooxygen to be gasified, and as a result, carbon is released from thesteel sheet. Thus, in the technologies described in Patent Documents 1to 3, the strength of the region of the steel sheet from which thecarbon is released is significantly decreased in some cases. In the casein which the strength of the surface of the steel sheet is decreased,there is a concern that fatigue resistance, which strongly depends onthe properties of the surface part, is deteriorated and thus fatiguelimit strength is significantly decreased.

Alternatively, in order to enhance the adhesion of a plated layer, inPatent Document 4, a method of enhancing plating adhesion by reformingthe surface of a base steel sheet in such a manner that steps areperformed by adding new annealing step and pickling step before a normalannealing step, is proposed. However, in the method described in PatentDocument 4, the number of steps is increased as compared to a normalmethod of producing a high strength plated steel sheet, and thus thereis a problem in costs.

Further, in Patent Document 5, a method of enhancing plating adhesion byremoving carbon from the surface part of a base steel sheet is proposed.However, in the method described in Patent Document 5, the strength ofthe region from which carbon is removed is significantly decreased. Inthis case, there is a concern that fatigue resistance, which stronglydepends on the properties of the surface part, is deteriorated and thusfatigue limit strength is significantly decreased in the methoddescribed in Patent Document 5.

In Patent Documents 6 and 7, there are disclosed steel sheets in whichthe amounts of Mn, Al, and Si in a plated layer are controlled to bewithin a suitable range and plating adhesion is improved. For the steelsheets described in these Patent Documents 6 and 7, it is required tocontrol the amounts of elements in the plated layer with high accuracyat the time of production, which applies a great industrial load andcauses a problem in costs.

In Patent Document 8, a high strength steel sheet in which themicrostructure of the steel sheet is formed of only ferrite is proposedas a method for enhancing plating adhesion. However, since themicrostructure is formed of only soft ferrite in the steel sheetdescribed in Patent Document 8, sufficiently high strength cannot beobtained.

Here, a galvannealed steel sheet obtained by subjecting a steel sheet toan alloying treatment after a hot dip galvanizing treatment is widelyused. The alloying treatment is a treatment of heating a plated layer toa temperature of equal to or higher than the melting point of Zn,diffusing a large amount of Fe atoms into the plated layer from theinside of a base steel sheet, and forming the plated layer into a layermainly including a Zn—Fe alloy. For example, in Patent Documents 9, 10and 11, galvannealed steel sheets excellent in plating adhesion areproposed. However, in the galvannealed steel sheets of Patent Documents9 to 11, it is required to heat a steel sheet at a high temperature soas to sufficiently alloy the plated layer. When the steel sheet isheated to a high temperature, the microstructure inside the steel sheetis reformed and particularly coarse iron-based carbides are easilygenerated and the properties of the steel sheet deteriorate. Thus, thiscase is not preferable.

In Patent Document 12, in the production of the hot-dip galvanized steelsheet of the base steel sheet containing Si—Mn—Al, by controlling of theentering temperature and defining the area fraction of the cross sectionof the alloy layer formed at the interface between the base steel sheetand the plated layer, the technology for improving plating adhesion andspot weldability is disclosed.

In the steel sheet described in Patent Document 12, it is disclosed thatSi—Mn oxides adversely affect on plating adhesion. However, a technologyfor reducing the amounts of Si—Mn oxides until plating is started is notdisclosed in Patent Document 12. In addition, in Patent Document 12, thetemperature at which the base steel sheet enters a plating bath is setto be higher than the temperature of the hot dip galvanizing bath (Thetemperature varies depending on the Al content in the hot dipgalvanizing bath, the temperature at which the base steel sheet enters aplating bath is set to be at least 4° C. higher than temperature of thehot dip galvanizing bath and to be at most 28° C. higher thantemperature of the hot dip galvanizing bath.), therefore regarding thestability of the bath temperature, and uniformity in the properties ofthe product is not sufficient in some cases.

PRIOR ART DOCUMENT Patent Document

-   [Patent Document 1] Japanese Unexamined Patent Application, First    Publication No. 2008-019465-   [Patent Document 2] Japanese Unexamined Patent Application, First    Publication No. 2005-060742-   [Patent Document 3] Japanese Unexamined Patent Application, First    Publication No. H9-176815-   [Patent Document 4] Japanese Unexamined Patent Application, First    Publication No. 2001-026853-   [Patent Document 5] Japanese Unexamined Patent Application, First    Publication No. 2002-088459-   [Patent Document 6] Japanese Unexamined Patent Application, First    Publication No. 2003-055751-   [Patent Document 7] Japanese Unexamined Patent Application, First    Publication No. 2003-096541-   [Patent Document 8] Japanese Unexamined Patent Application, First    Publication No. 2005-200750-   [Patent Document 9] Japanese Unexamined Patent Application, First    Publication No. H11-140587-   [Patent Document 10] Japanese Unexamined Patent Application, First    Publication No. 2001-303226-   [Patent Document 11] Japanese Unexamined Patent Application, First    Publication No. 2005-060743-   [Patent Document 12] Published Japanese Translation No. 2013-541645    of the PCT International Publication

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In consideration of the above circumstances, an object of the presentinvention is to provide a high strength hot-dip galvanized steel sheetexcellent in formabilities of a steel sheet, which are represented byductility, bendability and stretch-flange formability and excellent infatigue resistance, weldability, corrosion resistance and platingadhesion.

Means for Solving the Problem

The present inventors have conducted intensive investigations forobtaining a high strength hot-dip galvanized steel sheet excellent informabilities of a steel sheet represented by ductility, bendability andstretch-flange formability and excellent in fatigue resistance,weldability, corrosion resistance and plating adhesion. As a result, thepresent inventors have improved ductility and hole expansibility(stretch-flange property) by controlling microstructures of a steelsheet in an appropriate structure fraction. In addition, the presentinventors have improved bendability and fatigue resistance bycontrolling a volume fraction of a hard phase at the side of the basesteel sheet of an interface between a plating layer and the base steelsheet. The present inventors have suppressed plating peeling by forminga ζ phase (FeZn₁₃) in a plated layer and incorporating a coarse oxide,which acts as a fracture origin, in the inside thereof. By the abovemethod, the present inventors have found that a hot-dip galvanized steelsheet excellent in formabilities of a steel sheet represented byductility, bendability and hole expansibility (stretch-flange property)and excellent in fatigue resistance, weldability, corrosion resistanceand plating adhesion can be obtained without subjecting the platinglayer to an alloying treatment.

The present invention has been completed based on the findings andaspects thereof are as follows.

(1) A hot-dip galvanized steel sheet according to an aspect of thepresent invention, is a hot-dip galvanized steel sheet comprising: abase steel sheet; and

a hot-dip galvanized layer formed on at least one surface of the basesteel sheet, wherein: the base steel sheet includes, a chemicalcomposition comprising, % by mass,

C: 0.040% to 0.280%,

Si: 0.05% to 2.00%,

Mn: 0.50% to 3.50%,

P: 0.0001% to 0.1000%,

S: 0.0001% to 0.0100%,

Al: 0.001% to 1.500%,

N: 0.0001% to 0.0100%,

O: 0.0001% to 0.0100%, and

a remainder of Fe and impurities;

in a range of ⅛ thickness to ⅜ thickness centered at a position of ¼thickness from the surface of the base steel sheet, by volume fraction,40% or more and 97% or less of a ferrite phase, a total of 3% or more ofa hard structure comprising one or more of a bainite phase, a bainiticferrite phase, a fresh martensite phase and a tempered martensite phase,a residual austenite phase is 0 to 8% by volume fraction, a total of apearlite phase and a coarse cementite phase is 0 to 8% by volumefraction, in a surface layer range of 20 μm depth in a steel sheetdirection from an interface between the hot-dip galvanized layer and thebase steel sheet, a volume fraction of a residual austenite is 0 to 3%,the base steel sheet includes a microstructure in which V1/V2 which is aratio of a volume fraction V1 of the hard structure in the surface layerrange and a volume fraction V2 of the hard structure in the range of ⅛thickness to ⅜ thickness centered at the position of ¼ thickness fromthe surface of the base steel sheet is 0.10 or more and 0.90 or less, aFe content is more than 0% to 5.0% or less and an Al content is morethan 0% to 1.0% or less in the hot-dip galvanized layer, and columnargrains formed of a ζ phase are included in the hot-dip galvanized layer,a ratio ((A*/A)×100) of an interface (A*) between the ζ phase and thebase steel sheet in an entire interface (A) between the hot-dipgalvanized plated layer and the base steel sheet is 20% or more, arefined layer is formed at the side of the interface in the base steelsheet, an average thickness of the refined layer is 0.1 to 5.0 μm, anaverage grain size of ferrite in the refined layer is 0.1 to 3.0 μm, oneor two or more of oxides of Si and Mn are contained, and a maximum sizeof the oxide is 0.01 to 0.4 μm.

(2) The hot-dip galvanized steel sheet according to the above (1),wherein the base steel sheet further contains, % by mass, one or two ormore selected from

Ti: 0.001% to 0.150%,

Nb: 0.001% to 0.100%, and

V: 0.001% to 0.300%.

(3) The hot-dip galvanized steel sheet according to the above (1) or(2), wherein the base steel sheet contains, % by mass, one or two ormore selected from

Cr: 0.01% to 2.00%,

Ni: 0.01% to 2.00%,

Cu: 0.01% to 2.00%,

Mo: 0.01% to 2.00%,

B: 0.0001% to 0.0100%, and

W: 0.01% to 2.00%.

(4) The hot-dip galvanized steel sheet according to any one of the above(1) to (3), wherein the base steel sheet contains, % by mass, one or twoor more selected from Ca, Ce, Mg, Zr, La, and REM in a total amount of0.0001% to 0.0100%.

(5) The hot-dip galvanized steel sheet according to any one of the above(1) to (4), wherein a ratio of an interface formed between ζ grains inwhich coarse oxides are present and the base steel sheet in an interfacebetween the ζ phase and the base steel sheet in the hot-dip galvanizedlayer is 50% or less.

(6) The hot-dip galvanized steel sheet according to any one of the above(1) to (5), wherein a plated amount on one surface of the base steelsheet in the hot-dip galvanized layer is 10 g/m² or more and 100 g/m² orless.

Effects of the Invention

According to the above aspects of the present invention, it is possibleto provide a hot-dip galvanized steel sheet excellent in formability,fatigue resistance, weldability, corrosion resistance and platingadhesion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged structure micrograph of the vicinity of an areaincluding an interface between a hot-dip galvanized layer and a basesteel sheet in the cross section of a hot-dip galvanized steel sheetaccording to an embodiment.

FIG. 2 is an enlarged cross section structure micrograph of the vicinityof an area including an interface between a hot-dip galvanized layer anda base steel sheet in the cross section of a hot-dip galvanized steelsheet according to an example.

EMBODIMENTS OF THE INVENTION

A hot-dip galvanized steel sheet according to the embodiment is ahot-dip galvanized steel sheet which a hot-dip galvanized layer(hereinafter, also referred to as a plated layer simply) is formed on asurface of a base steel sheet (hereinafter, also referred to as a steelsheet simply) including a chemical composition which comprises, % bymass, C: 0.040% to 0.280%, Si: 0.05% to 2.00%, Mn: 0.50% to 3.50%, P:0.0001% to 0.1000%, S: 0.0001% to 0.0100%, Al: 0.001% to 1.500%, N:0.0001% to 0.0100%, O: 0.0001% to 0.0100%, and a remainder of Fe andimpurities.

It is appropriate that the thickness of the base steel sheet is 0.6 mmor more and less than 5.0 mm. When the thickness of the base steel sheetis less than 0.6 mm, it is difficult to keep the shape of the base steelsheet flat and the thickness is not appropriate. In addition, when thethickness of the base steel sheet is 5.0 mm or more, the control ofcooling in a production process will be difficult, a predeterminedmicrostructure is not obtained and formability deteriorates.

First, the chemical components (composition) of the base steel sheetconstituting the hot-dip galvanized steel sheet according to theembodiment will be described below. In the following description, theterm “%” means “% by mass”.

[C: 0.040% to 0.280%]

C is added to enhance the strength of the base steel sheet. However,when the C content is more than 0.280%, the spot weldability isdeteriorated. Thus, the C content is 0.280% or less. From the viewpointof spot weldability, the C content is preferably 0.250% or less and morepreferably 0.220% or less. On the other hand, when the C content is lessthan 0.040%, the strength is deteriorated and thus it is difficult tosecure sufficient maximum tensile strength. Thus, the C content is0.040% or more. In order to further increase the strength, the C contentis preferably 0.055% or more and more preferably 0.070% or more.

[Si: 0.05% to 2.00%]

Si is an element that suppresses formation of iron-based carbides in thebase steel sheet and enhances strength and formability. However, Si isan element that makes steel brittle. When the Si content is more than2.00%, a trouble such as cracking of a cast slab or the like easilyoccurs. Therefore, the Si content is 2.00% or less. Further, Si formsoxides on the surface of the base steel sheet in an annealing step tosignificantly impair plating adhesion. From this viewpoint, the Sicontent is preferably 1.500% or less and more preferably 1.200% or less.On the other hand, when the Si content is less than 0.05%, in a platingstep for the hot-dip galvanized steel sheet, a large amount of coarseiron-based carbides is formed and strength and formability deteriorate.Therefore, the Si content is 0.05% or more. From the viewpoint ofsuppressing formation of iron-based carbides, the Si content ispreferably 0.10% or more and more preferably 0.25% or more.

[Mn: 0.50% to 3.50%]

Mn is added to increase the strength by increasing the hardenability ofthe base steel sheet. However, when the Mn content is more than 3.50%, acoarse Mn-concentrated part is generated in the thickness central partof the base steel sheet and embrittlement easily occurs. Thus, a troublesuch as cracking of a cast slab easily occurs. Therefore, the Mn contentis 3.50% or less. In addition, an increase in the Mn content results indeterioration of spot weldability of the hot-dip galvanized steel sheet.For this reason, the Mn content is preferably 3.00% or less and morepreferably 2.80% or less. On the other hand, when the Mn content is lessthan 0.50%, a large amount of soft structure during cooling afterannealing is formed and thus it is difficult to secure a sufficientlyhigh maximum tensile strength. Accordingly, the Mn content is necessaryto be 0.50% or more. In order to further enhance strength of the hot-dipgalvanized steel sheet, the Mn content is preferably 0.80% or more andmore preferably 1.00% or more.

[P: 0.0001% to 0.1000%]

P is an element that makes steel brittle and when the P content is morethan 0.1000%, troubles such as cracking of a cast slab and cracking of aslab during hot rolling easily occurs. Therefore, the P content is0.1000% or less. In addition, P is an element that causes embrittlementof a molten part by spot welding, and the P content is preferably0.0400% or less and more preferably 0.0200% or less in order to obtainsufficient welded joint strength. On the other hand, a P content of lessthan 0.0001% results in a greatly increased production cost. Thus, it ispreferable that the P content has a lower limit of 0.0001% and the Pcontent is 0.0010% or more.

[S: 0.0001% to 0.0100%]

S is an element that is bounded to Mn and forms coarse MnS andformability such as ductility, hole expansibility (stretch-flangeproperty) and bendability deteriorates. Therefore, the S content is0.0100% or less. In addition, S is an element that deteriorates spotweldability. Therefore, the S content is preferably 0.0060% or less andmore preferably 0.0035% or less. On the other hand, a S content of lessthan 0.0001% results in a greatly increased production cost. Therefore,it is preferable that the S content has a lower limit of 0.0001%, andthe S content is 0.0005% or more, and more preferably 0.0010% or more.

[Al: 0.001% to 1.500%]

Al is an element that makes steel brittle. When the Al content is morethan 1.500%, a trouble such as cracking of a cast slab easily occurs andthus the Al content is 1.500% or less. In addition, when the Al contentis increased, spot weldability is deteriorated and thus the Al contentis more preferably 1.200% or less and even more preferably 1.000% orless. On the other hand, even when the lower limit of the Al content isnot particularly limited, the effects of the embodiment are exhibited.Al is an unavoidable impurity present in the raw material in a verysmall amount and an Al content of less than 0.001% results in a greatlyincreased production cost. Therefore, the Al content is 0.001% or more.In addition, Al is an element that that is effective as a deoxidationmaterial but in order to obtain a sufficient deoxidation effect, the Alcontent is more preferably 0.010% or more.

[N: 0.0001% to 0.0100%]

Since N is an element that forms a coarse nitride and deterioratesformability such as ductility, hole expansibility (stretch-flangeproperty) and bendability, the amount of N added is necessary to besuppressed. When the N content is more than 0.0100%, deterioration informability is significant and thus the upper limit of the N content is0.0100%. In addition, an excessive amount of N causes generation ofblowholes at the time of welding and the lower the content thereof isthe better it is. From this viewpoint, the N content is preferably0.0070% or less and more preferably 0.0050% or less. On the other hand,even when the lower limit of the N content is not particularly limited,the effects of the embodiment are exhibited. However, an N content ofless than 0.0001% results in a greatly increased production cost.Therefore, the lower limit of the N content is 0.0001% or more. The Ncontent is preferably 0.0003% or more and more preferably 0.0005% ormore.

[O: 0.0001% to 0.0100%]

Since O forms an oxide and deteriorates formability such as ductility,hole expansibility (stretch-flange property) and bendability of thehot-dip galvanized steel sheet, the content thereof is necessary to besuppressed. When the O content is more than 0.0100%, deterioration informability is significant and thus the upper limit of the upper limitof the O content is 0.0100%. Further, the O content is preferably0.0050% or less and more preferably 0.0030% or less. Even when the lowerlimit of the O content is not particularly limited, the effects of theembodiment are exhibited. However, an O content of less than 0.0001%results in a greatly increased production cost. Therefore, the lowerlimit thereof is 0.0001%. The O content is preferably 0.0003% or moreand more preferably 0.0005% or more.

Further, the following elements may be optionally added to the basesteel sheet of the hot-dip galvanized steel sheet according to theembodiment.

First, the base steel sheet according to the embodiment may furthercontain one or two or more selected from Ti: 0.001% to 0.150%, Nb:0.001% to 0.100%, and V: 0.001% to 0.300%.

[Ti: 0.001% to 0.150%]

Ti is an element that contributes to increasing the strength of thehot-dip galvanized steel sheet by precipitate strengthening, fine grainstrengthening due to suppression of ferrite grain growth, anddislocation strengthening through suppression of recrystallization.However, when the Ti content is more than 0.150%, the amount ofprecipitated carbonitrides is increased formability deteriorates. Thus,the Ti content is preferably 0.150% or less. In addition, from theviewpoint of formability, the Ti content is more preferably 0.080% orless. On the other hand, even when the lower limit of the Ti content isnot particularly limited, the effects of the embodiment are exhibited.However, in order to sufficiently obtain the effect ofhigh-strengthening by adding Ti, the Ti content is preferably 0.001% ormore. In order to achieve higher strength of the hot-dip galvanizedsteel sheet, the Ti content is more preferably 0.010% or more.

[Nb: 0.001% to 0.100%]

Nb is an element that contributes to increasing the strength of thehot-dip galvanized steel sheet by precipitate strengthening, fine grainstrengthening due to suppression of ferrite grain growth, anddislocation strengthening through suppression of recrystallization.However, when the Nb content is more than 0.100%, the amount ofprecipitated carbonitrides is increased and formability of the hot-dipgalvanized steel sheet deteriorates. Thus, the Nb content is morepreferably 0.100% or less. From the viewpoint of formability, the Nbcontent is more preferably 0.060% or less. On the other hand, even whenthe lower limit of Nb content is not particularly limited, the effectsof the embodiment are exhibited. However, in order to obtain asufficiently obtain the effect of high-strengthening by adding Nb, theNb content is preferably 0.001% or more. In order to achieve higherstrength of the hot-dip galvanized steel sheet, the Nb content is morepreferably 0.005% or more.

[V: 0.001% to 0.300%]

V is an element that contributes to increasing the strength of thehot-dip galvanized steel sheet by precipitate strengthening, fine grainstrengthening due to suppression of ferrite grain growth, anddislocation strengthening through suppression of recrystallization.However, when the V content is more than 0.300%, the amount ofprecipitated carbonitrides is increased and formability deteriorates.Therefore, the V content is preferably 0.300% or less and morepreferably 0.200% or less. On the other hand, even when the lower limitof the V content is not particularly limited, the effects of theembodiment are exhibited. In order to sufficiently obtain the effect ofhigh-strengthening by adding V, the V content is preferably 0.001% ormore and more preferably 0.010% or more.

In addition, the base steel sheet according to the embodiment maycontain one or two or more selected from Cr 0.01 to 2.00%, Ni: 0.01% to2.00%, Cu: 0.01% to 2.00%, Mo: 0.01% to 2.00%, B: 0.0001% to 0.0100%,and W: 0.01% to 2.00%.

[Cr 0.01% to 2.00%]

Cr is an element that suppresses phase transformation at a hightemperature and is effective for high-strengthening of the hot-dipgalvanized steel sheet and may be added instead of part of C and/or Mn.However, when the Cr content is more than 2.00%, hot workability isimpaired and productivity deteriorates. Thus, the Cr content ispreferably 2.00% or less and more preferably 1.20% or less. On the otherhand, even when the lower limit of the Cr content is not particularlylimited, the effects of the embodiment are exhibited. However, in orderto sufficiently obtain the effect of high-strengthening by adding Cr,the Cr content is preferably 0.01% or more and more preferably 0.10% ormore.

[Ni: 0.01% to 2.00%]

Ni is an element that suppresses phase transformation at a hightemperature and is effective for high-strengthening of the hot-dipgalvanized steel sheet and may be added instead of part of C and/or Mn.However, when a Ni content is more than 2.00%, weldability is impaired.Thus, the Ni content is preferably 2.00% or less and more preferably1.20% or less. On the other hand, even when the lower limit of the Nicontent is not particularly limited, the effects of the embodiment areexhibited. However, in order to sufficiently obtain the effect ofhigh-strengthening by adding Ni, the Ni content is preferably 0.01% ormore and more preferably 0.10% or more.

[Cu: 0.01% to 2.00%]

Cu is an element that that exists as fine particles in steel to therebyenhance strength of the hot-dip galvanized steel sheet and can be addedinstead of part of C and/or Mn. However, when the Cu content is morethan 2.00%, weldability is impaired. Thus, the Cu content is preferably2.00% or less and more preferably 1.20% or less. On the other hand, evenwhen the lower limit of the Cu content is not particularly limited, theeffects of the embodiment are exhibited. However, in order tosufficiently obtain the effect of high-strengthening of the hot-dipgalvanized steel sheet by adding Cu, the Cu content is preferably 0.01%or more and more preferably 0.10% or more.

[Mo: 0.01% to 2.00%]

Mo is an element that suppresses phase transformation at a hightemperature and is effective for high-strengthening of the hot-dipgalvanized steel sheet and may be added instead of part of C and/or Mn.However, when the Mo content is more than 2.00%, hot workability isimpaired and productivity deteriorates. Thus, the Mo content ispreferably 2.00% or less and more preferably 1.20% or less. On the otherhand, even when the lower limit of the Mo content is not particularlylimited, the effects of the embodiment are exhibited. However, in orderto sufficiently obtain the effect of high-strengthening by adding Mo,the Mo content is preferably 0.01% or more and more preferably 0.05% ormore.

[B: 0.0001% to 0.0100%]

B is an element that suppresses phase transformation at a hightemperature and is effective for high-strengthening of the hot-dipgalvanized steel sheet and may be added instead of part of C and/or Mn.However, when the B content is more than 0.0100%, hot workability isimpaired and productivity deteriorates. Thus, the B content ispreferably 0.0100% or less. From the viewpoint of productivity, the Bcontent is more preferably 0.0050% or less. On the other hand, even whenthe lower limit of the B content is not particularly limited, theeffects of the embodiment are exhibited. However, in order tosufficiently obtain the effect of high-strengthening by adding B, the Bcontent is preferably 0.0001% or more. In order to achieve furtherhigh-strengthening of the hot-dip galvanized steel sheet, the B contentis more preferably 0.0005% or more.

[W: 0.01% to 2.00%]

W is an element that suppresses phase transformation at a hightemperature and is effective for high-strengthening of the hot-dipgalvanized steel sheet and may be added instead of part of C and/or Mn.However, when the W content is more than 2.00%, hot workability isimpaired and productivity deteriorates. Thus, the W content ispreferably 2.00% or less and more preferably 1.20% or less. On the otherhand, even when the lower limit of the W content is not particularlylimited, the effects of the embodiment are exhibited. However, in orderto sufficiently obtain the effect of high-strengthening by adding W, theW content is preferably 0.01% or more and more preferably 0.10% or more.

The base steel sheet in the hot-dip galvanized steel sheet according tothe embodiment may further contain, as another elements, one or two ormore of Ca, Ce, Mg, Zr, La, and REM in a total amount of 0.0001% to0.0100%. The reasons for adding these elements are as follows.

Note that REM stands for Rare Earth Metal and refers to an elementbelonging to the lanthanoid series. In this embodiment, REM or Ce isoften added in misch metal and may contain elements of the lanthanoidseries other than La and Ce in a complex form. The effects of theembodiment are exhibited even when elements of the lanthanoid seriesother than La and Ce are contained in the slab as impurities. Further,the effects of the embodiment are exhibited even when metals La and Ceare added to the slab.

Ca, Ce, Mg, Zr, La, and REM are elements effective for improvingformability of the hot-dip galvanized steel sheet, and one or two ormore of these elements can be added to the slab. However, when the totalcontent of one or two or more of Ca, Ce, Mg, Zr, La, and REM is morethan 0.0100%, there is a concern of ductility being impaired. Therefore,the total content of the respective elements is preferably 0.0100% orless and more preferably 0.0070% or less. On the other hand, even whenthe lower limit of the content of one or two or more of Ca, Ce, Mg, Zr,La, and REM is not particularly limited, the effects of the embodimentare exhibited. However, in order to sufficiently obtaining the effect ofimproving the formability of the hot-dip galvanized steel sheet, thetotal content of one or two or more of the respective elements ispreferably 0.0001% or more. From the viewpoint of formability, the totalcontent of one or two or more of Ca, Cc, Mg, Zr, La, and REM is morepreferably 0.0010% or more.

In the chemical components of the hot-dip galvanized steel sheetaccording to the embodiment, a remainder other than the above-describedrespective elements includes Fe and impurities. Incidentally, a verysmall amount of each of Ti, Nb, V, Cr, Ni, Cu, Mo, B, and W describedabove being less than the above-described lower limit value is allowedto be contained as an impurity. In addition, regarding Ca, Ce, Mg, Zr,La, and REM, a minute amount of them being less than the above-describedlower limit value of the total content of them is allowed to becontained as an impurity.

The reasons for defining the structure of the base steel sheet of thehot-dip galvanized steel sheet according to the embodiment of thepresent invention are as follows.

(Microstructure)

The microstructure in the base steel sheet of the hot-dip galvanizedsteel sheet according to the embodiment of the present invention is amicrostructure in which, in a range of ⅛ thickness to ⅜ thicknesscentered at a position of ¼ thickness from the surface of the base steelsheet, a ferrite phase (hereinafter, referred to as a ferrite) is 40% ormore and 97% or less by volume fraction, a hard structure comprising oneor more of a bainite phase (hereinafter, referred to as a bainite), abainitic ferrite phase (hereinafter, referred to as a bainitic ferrite),a fresh martensite phase (hereinafter, referred to as a martensite) anda tempered martensite phase (hereinafter, referred to as a temperedmartensite) in total is 3% or more by volume fraction, a residualaustenite phase (hereinafter, referred to as an residual austenite) is 0to 8% by volume fraction (including 0%), a pearlite phase (hereinafter,referred to as a pearlite) and a coarse cementite phase (hereinafter,referred to as a cementite) in total is 0 to 8% by volume fraction(including 0%).

[Ferrite]

Ferrite is a structure which has excellent ductility. However, since theferrite has low strength due to being soft, a hot-dip galvanized steelsheet having sufficient maximum tensile strength can not be obtainedwhen the volume fraction of the ferrite is more than 97%. Therefore, thevolume fraction of the ferrite is 97% or less. In order to improvemaximum tensile strength of the hot-dip galvanized steel sheet, thevolume fraction of the ferrite is preferably 92% or less and morepreferably 85% or less. Further, in order to obtain a hot-dip galvanizedsteel sheet having a maximum tensile strength of more than 950 MPa, thevolume fraction of the ferrite is preferably 80% or less and morepreferably 70% or less. On the other hand, sufficient ductility can notbe obtained when the volume fraction of the ferrite is less than 40%.Therefore, the volume fraction of the ferrite is 40% or more. The volumefraction of the ferrite is preferably 45% or more and more preferably50% or more.

[Residual Austenite]

The residual austenite is a structure for greatly improving a balancebetween strength and ductility of the hot-dip galvanized steel sheet. Onthe other hand, the residual austenite is transformed into hardmartensite with deformation and this hard martensite acts as a fractureorigin, and stretch-flange property deteriorates. Thus, an upper limitof the volume fraction of the residual austenite is 8%. From theviewpoint of formability of the hot-dip galvanized steel sheet, thevolume fraction of the residual austenite is preferably low and 5% orless, and more preferably 0 to 3% (including 0%). The volume fraction ofthe residual austenite of the hot-dip galvanized steel sheet ispreferably lower and may be 0%.

[Hard Structure]

In order to improve maximum tensile strength of the hot-dip galvanizedsteel sheet, it is necessary that a volume fraction of the hardstructure comprising one or more of a bainite, a bainitic ferrite, afresh martensite and a tempered martensite in total is 3% or more. Inorder to improve maximum tensile strength of the hot-dip galvanizedsteel sheet, the volume fraction of the hard structure is preferably 7%or more and more preferably 15% or more. On the other hand, since theductility of the hot-dip galvanized steel sheet deteriorates when thevolume fraction of the hard structure is excessively high, the volumefraction of the hard structure is limited to 60% or less. From thisviewpoint, the volume fraction of the hard structure is preferably 55%or less and more preferably 50% or less.

[Bainitic Ferrite and/or Bainite]

Bainitic ferrite and/or bainite are a structure excellent in a balancebetween strength and formability of the hot-dip galvanized steel sheet.It is preferable that the bainitic ferrite and/or the bainite areincluded 60% or less by volume fraction, in a steel sheet structure. Inaddition, the bainitic ferrite and/or the bainite are microstructureswhich have medial strength between a soft ferrite and a hard martensite,a tempered martensite and a residual austenite, are more preferablyincluded 5% or more and are even more preferably included 10% or more,in viewpoint of stretch-flange property. On the other hand, yield stressexcessively increases when the volume fraction of the bainitic ferriteand/or the bainite are more than 60%. Therefore, it is not preferablebecause the shape freezing property is concerned to deteriorate.

[Tempered Martensite]

Tempered martensite is a structure which increases tensile strength ofthe hot-dip galvanized steel sheet greatly and may be included 60% orless by volume fraction, in the steel sheet structure. From viewpoint oftensile strength, it is preferable that the volume fraction of thetempered martensite is 5% or more. On the other hand, yield stressexcessively increases when the volume fraction of the bainitic ferriteand/or the bainite are more than 60%. Therefore, it is not preferablebecause the shape freezing property is concerned to deteriorate.

[Fresh Martensite]

Fresh martensite increases tensile strength of the hot-dip galvanizedsteel sheet greatly. On the other hand, the fresh martensite works as afracture origin, and deteriorates stretch-flange property. Therefore, itis preferable that the fresh martensite is included in the steel sheetstructure, by a volume fraction of 30% or less. In order to increasehole expansibility, the volume fraction of the fresh martensite is morepreferably 20% or less and even more preferably 10% or less.

[Other Microstructures]

Microstructures other than the above described microstructures, such aspearlite and/or coarse cementite, may be included in the steel sheetstructure of the hot-dip galvanized steel sheet according to theembodiment of the present invention. However, ductility deteriorateswhen the content of the pearlite and/or the coarse cementite in thesteel sheet structure of the hot-dip galvanized steel sheet increases.From this viewpoint, a volume fraction of the pearlite and/or the coarsecementite in the steel sheet structure is 8% or less in total. A totalof the content of the pearlite and/or the coarse cementite is preferably5% or less.

Further, in the steel sheet structure of the hot-dip galvanized steelsheet according to the embodiment of the present invention, the volumefraction of the residual austenite is limited to 3% or less in a surfacelayer range originating from an interface between a plated layer and abase steel sheet (base steel) and having 20 m depth in a steel sheetdirection. And further, a volume fraction “V1” of the hard structure inthe surface layer range is in a range of 0.10 to 0.90 times of a volumefraction “V2” of the hard structure in a range of ⅛ thickness to ⅜thickness centered at a position of ¼ thickness from the surface of thebase steel sheet.

[Residual Austenite in Vicinity of Interface of Plated Layer and BaseSteel]

Residual austenite in the vicinity of the interface of the plated layerof the hot-dip galvanized steel sheet and the base steel sheet istransformed into hard martensite with deformation and acts as a fractureorigin at the time of bending deformation in which a large strain isadded in the vicinity of a surface of the hot-dip galvanized steelsheet. Therefore, the residual austenite in the vicinity of theinterface of the plated layer of the hot-dip galvanized steel sheet andthe base steel sheet is a structure which influences deterioration ofbendability and fatigue resistance. Form this viewpoint, it is necessarythat the volume fraction of the residual austenite is limited to 0 to 3%(including 0%) in a surface layer range originating from an interfacebetween a plated layer and a base steel sheet (base steel) and having 20μm depth in a steel sheet direction. The volume fraction of the residualaustenite in the above surface layer range is preferably lower and maybe 0%.

[Hard Structure in Vicinity of Interface of Plated Layer and Base Steel]

Hard structure in the vicinity of the interface of the plated layer ofthe hot-dip galvanized steel sheet and the base steel sheet (base steel)is a structure which enhances strength of the hot-dip galvanized steelsheet at the surface thereof, improves fatigue limit strength greatly,and influences improvement of fatigue resistance. From this viewpoint,when a volume fraction of the hard structure in a surface layer rangeoriginating from an interface between a plated layer and a base steeland having 20 μm depth in a steel sheet direction is set as “V1” and atotal volume fraction in a range of ⅛ thickness to ⅜ thickness centeredat a position of ¼ thickness from the surface of the base steel sheet isset as “V2”, V1/V2 which is a ratio of these is set to be 0.10 or more,and it is necessary to sufficiently enhance the strength of the hot-dipgalvanized steel sheet at the surface thereof. In order to sufficientlyimprove fatigue resistance, V1/V2 is preferably 0.20 or more, morepreferably 0.30 or more and even more preferably 0.40 or more. On theother hand, bendability can be improved, by controlling a fraction ofthe hard structure in a surface layer range originating from aninterface between a plated layer and a base steel and having 20 μm depthin a steel sheet direction to a certain degree and decreasing strengthin the vicinity of the surface of the hot-dip galvanized steel sheet andimproving ductility partially. From this viewpoint, in order to obtaingood bendability, V1/V2 is 0.90 or less, preferably 0.85 or less andmore preferably 0.80 or less.

Further, in the surface layer range originating from an interfacebetween a plated layer of the hot-dip galvanized steel sheet accordingto the embodiment and a base steel and having 20 μm depth in a steelsheet direction, BCC grain boundaries of Fe and/or fine oxides includingSi and/or Mn in grains may be contained. Formation of oxides includingSi and/or Mn can be suppressed at the surface of the steel sheet whichacts as the origin of peeling of the plated layer, the interface betweenthe plated layer and a base steel sheet in other words, by antecedentlyforming fine oxides inside of the steel sheet at the surface layer rangethereof.

The volume fraction of each structure contained in the base steel sheetof the hot-dip galvanized steel sheet according to the embodiment of thepresent invention can be measured by the method, for example describedbelow.

The volume fraction of each of ferrite, bainitic ferrite, bainite,tempered martensite, fresh martensite, pearlite, and coarse cementiteincluded in the steel sheet structure of the hot-dip galvanized steelsheet according to the present invention is determined as describedbelow. The thickness cross section parallel to the rolling direction ofthe steel sheet is set as an observed section and a sample is collected,and the observed section of the sample is polished and etched withnital. The range of ⅛ thickness to ⅜ thickness centered at the positionof ¼ of the thickness from the surface of the base steel sheet or therange of originating from an interface between a plated layer and a basesteel sheet (base steel) and having 20 μm depth in a steel sheetdirection are respectively observed with a field emission scanningelectron microscope (FE-SEM) to measure the area fractions of thestructures and these area fractions can be considered as the volumefractions of the respective structures. However, when the plated layeris removed by the nital etching, a surface of the sample can beconsidered as the interface between the plated layer and the base steel.

The volume fraction of residual austenite included in the steel sheetstructure of the hot-dip galvanized steel sheet according to theembodiment is evaluated, by performing high resolution crystalorientation analysis according to EBSD (Electron Bach-scatteringDiffraction) method using a FE-SEM.

First, a thickness cross section parallel to the rolling direction issubjected to mirror polishing, in the range of ⅛ thickness to ⅜thickness centered at the position of ¼ of the thickness from thesurface of the base steel sheet or in the range of originating from theinterface between the plated layer and the base steel and having 20 μmdepth in a steel sheet direction respectively, an observation step isset to be 0.15 μm or less, and crystal orientations are observed in arange of 10000 μm² or more in total. Each observation point isdetermined whether it is steel of BCC (Body-centered Cubic) or steel ofFCC (Face-centered Cubic), a point determined as FCC steel is set as aresidual austenite and an area fraction of the residual austenite ismeasured. This area fraction can be considered as the volume fraction.The area fraction and the volume fraction are equivalent when asufficient broad range is observed, in the above case, the area fractionof the residual austenite can be considered as the volume fractionthereof by observing crystal orientations in the range of 10000 μm² ormore in total.

The hot-dip galvanized steel sheet according to the embodiment has arefined layer in the base steel sheet at a side of interface contact tothe plated layer. A part of the refined layer which is close to theplated layer directly contacts with the plated layer. The refined lateris a region exists at an outermost layer of the base steel sheet and therefined later is a region in which the average grain size of ferritephase constituting the refined layer is ½ or less of the average grainsize of the ferrite phase in the lower layer of the refined layer in thebase steel sheer. The boundary at which the average grain size of theferrite in the refined layer is greater than ½ of the average grain sizeof the ferrite in the lower layer thereof is defined as a boundarybetween the refined later and the lower layer thereof.

The refined layer is in direct contact with the interface between thebase steel sheet and the hot-dip galvanized layer. The average thicknessof the refined layer is 0.1 to 5.0 μm. The average grain size of theferrite in the refined layer is 0.1 to 3.0 μm. The refined layercontains one or two or more of oxides of Si and Mn and the maximum sizeof the oxide is 0.01 to 0.4 μm.

When the average thickness of the refined layer is 0.1 μm or more, crackgeneration or extension is suppressed at the time of working the hot-dipgalvanized steel sheet. Therefore, the average thickness of the refinedlayer is 0.1 μm or more and is preferably 1 μm. In addition, when theaverage thickness of the refined layer is 5.0 μm or less, formation canbe processed while suppressing excessive alloying in a plating bath.Accordingly, it is possible to prevent deterioration in plating adhesioncaused by an excessive Fe content in the plated layer. For this reason,the average thickness of the refined layer is 5.0 μm or less andpreferably 3.0 μm or less.

When the average grain size of the ferrite in the refined layer is 0.1μm or more, cracking generation or extension is suppressed at the timeof working the hot-dip galvanized steel sheet. Therefore, the averagegrain size of the ferrite in the refined layer is 0.1 μm or more and ismore preferably 1 μm or more. In addition, when the average grain sizeof the ferrite in the refined layer is greater than 3.0 μm, the effectof suppressing crack generation or extension is limitative. Therefore,the average grain size of the ferrite in the refined layer is 3.0 μm orless and preferably 2.0 μm or less.

Examples of one or two or more of oxides of Si and Mn contained in therefined layer include one or two or more selected from SiO₂, Mn₂SiO₄,MnSiO₃, Fe₂SiO₄, FeSiO₃, and MnO.

When the maximum size of one or two or more of oxides of Si and Mncontained in the refined layer is 0.01 μm or more, the plated layer inwhich the formation of a ζ phase sufficiently proceeds with theformation of a refined layer can be formed. The maximum size of theoxide is preferably 0.05 μm or more. In addition, the refined layer inwhich the maximum size of the oxide is 0.4 μm or less can be formedwhile suppressing excessive alloying of the plated layer. Further, whenthe maximum size of the above oxides is 0.4 μm or less, formation can beprocessed while suppressing excessive alloying of the plated layer.Accordingly, it is possible to prevent deterioration in plating adhesioncaused by an excessive Fe content in the plated layer with a formationof the plated layer. The maximum size of the oxide is preferably 0.2 μmor less.

The average thickness of the refined layer and the average grain size ofthe ferrite in the refined layer are measured according to the methoddescribed below. A thickness cross section parallel to the rollingdirection of the base steel sheet is set as an observed section and asample is collected from the hot-dip galvanized steel sheet. Theobserved section of the sample is processed by using CP (Cross sectionpolisher) and a backscattered electron image is observed at amagnification of 5,000 with FE-SEM (Field Emission Scanning ElectronMicroscopy) for measurement.

The maximum size of one or two or more of oxides of Si and Mn containedin the refined layer is measured according to the method describedbelow. A thickness cross section parallel to the rolling direction ofthe base steel sheet is set as an observed section and samples arecollected from the hot-dip galvanized steel sheet.

The observed section of each sample is processed with FIB (Focused IonBeam) to prepare thin film samples. Thereafter, each thin film sample isobserved with FE-TEM (Field Emission Transmission Electron Microscopy)at a magnification of 30,000. Each thin film sample is observed in fivevisual fields and the maximum size of the diameter of the oxide measuredin the whole visual field is set as the maximum size of the oxide in thethin film sample.

[Plated Layer]

The hot-dip galvanized steel sheet according to the embodiment of thepresent invention is a hot-dip galvanized steel sheet which a hot-dipgalvanized layer is formed on a surface of a base steel sheet.

In the embodiment of the present invention, a Fe content is more than 0%to 5.0% or less and an Al content is more than 0% to 1.0% or less in thehot-dip galvanized layer. Furthermore, the hot-dip galvanized layer maycontain one or two or more of Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge,Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Rb, Sb, Si, Sn, Sr, Ta,Ti, V, W, Zr, and REM or one or two or more of these elements are mixedin the hot-dip galvanized layer. Even when the hot-dip galvanized layercontains one or two or more of these elements or one or two or more ofthese elements are mixed in the hot-dip galvanized layer as describedabove, the effects of the embodiment are not deteriorated and there issometimes a preferable case in which the corrosion resistance and theworkability are improved depending on the content of the element.

Further, the hot-dip galvanized layer includes columnar grains formed ofa ζ phase and 20% or more of it is covered with a ζ phase in the entireinterface between the plated layer and the base steel. Thus, the ratio((A*/A)×100) of the interface (A*) between the above ζ phase and thebase steel sheet is 20% or more in the entire interface (A) between thehot-dip galvanized plated layer and the base steel sheet. Further, aplated amount on one surface of the base steel sheet in the hot-dipgalvanized layer is 10 g/m² or more and 100 g/m² or less.

[Fe Content in Hot-Dip Galvanized Layer More than 0% to 5.0% or Less]

Since the plating adhesion is deteriorated when the Fe content in thehot-dip galvanized layer becomes higher, it is necessary that the Fecontent is more than 0% to 5.0% or less. In order to further enhance theplating adhesion, the Fe content in the plated layer is preferably 4.0%or less and more preferably 3% or less. The lower limit of the Fecontent in the plated layer is not limited. However, when the Fe contentis less than 0.5%, since the amount of ζ phase required to enhanceadhesion is not sufficiently obtained in some cases, the Fe content inthe plated layer is preferably 0.5% or more and more preferably 1.0% ormore.

[Al Content in Hot-Dip Galvanized Layer: More than 0% to 1.0% or Less]

Since the plating adhesion is deteriorated when the Al content in thehot-dip galvanized layer becomes higher, it is necessary that the Alcontent is more than 0% to 1.0% or less. In order to further enhance theplating adhesion, the Al content in the plated layer is preferably 0.8%or less and more preferably 0.5% or less. The lower limit of the Alcontent in the plated layer is not limited. However, in order to set theAl content to less than 0.01%, it is required that the concentration ofAl in a plating bath is lowered extremely. When the concentration of Alin a plating bath is lowered extremely, the alloying of the plated layerexcessively proceeds and thus the Fe content in the plated layer isincreased. And therefore, the plating adhesion deteriorates. For thisreason, the Al content in the plated layer is preferably 0.01% or more.From this viewpoint, the Al content in the plated layer is morepreferably 0.05% or more.

Furthermore, the hot-dip galvanized layer may contain one or two or moreof Ag. B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, I, K, La, Li, Mg, Mn,Mo, Na, Nb, Ni, Pb, Rb, Sb, Si, Sn, Sr, Ta, Ti, V. W, Zr, and REM or oneor two or more of these elements are mixed in the hot-dip galvanizedlayer. Even when the hot-dip galvanized layer contains one or two ormore of these elements or one or two or more of these elements are mixedin the hot-dip galvanized layer as described above, the effects of theembodiment are not deteriorated and there is sometimes a preferable casein which the corrosion resistance and the workability are improveddepending on the content of the element.

[ζ Phase]

FIG. 1 indicates an enlarged structure micrograph of a cross section ofthe hot-dip galvanized steel sheet according to the embodiment. As shownin FIG. 1, the hot-dip galvanized layer of the embodiment is a platedlayer plated on the surface of the base steel sheet (base steel), andincludes columnar grains formed of a ζ phase (FeZn₁₃) of an alloy of Feand Zn. Particularly, in the hot-dip galvanized layer of the embodiment,the ratio ((A*/A)×100) of the interface (A*) of the ζ phase in contactwith the base steel sheet is 20% or more in the entire interface (A)between the hot-dip galvanized plated layer and the base steel sheet.

Accordingly, coarse oxides including Si and/or Mn, which act as theorigin of peeling, and having a major axis of 0.2 μm or more areincorporated into the (phase from the surface of the base steel sheet.This makes the coarse oxides hardly work as a fracture origin and thusthe adhesion of the plated layer is improved. From this viewpoint, theratio of the interface between the ζ phase and the base steel withrespect to the entire interface between the plated layer and the basesteel sheet is preferably 25% or more and more preferably 30% or more.The upper limit of the ratio of the interface between the ζ phase andthe base steel sheet with respect to the entire interface between theplated layer and the base steel is not particularly limited and may be100%.

On the other hand, when the coarse oxides including Si and/or Mn andhaving the major axis of 0.2 μm or more are not incorporated into the ζphase and the coarse oxides are present at the interface between the ζphase and the base steel sheet, the effect of improving plating adhesionby the ζ phase cannot be sufficiently obtained and is not preferable.For this reason, the ratio of the interface between ζ grains (coarseoxide-containing ζ grains) in which coarse oxides are present among theζ grains and the base steel sheet is preferably 50% or less, and morepreferably 35% or less, with respect to the entire interface between theζ phase and the base steel sheet. It is more preferable that the amountof the coarse oxides at the interface of the base steel sheet of the ζphase is smaller. In the entire interface between the ζ phase and thebase steel sheet, the ratio of the interface formed between the coarseoxide-containing ζ grain and the base steel sheet in the interfacebetween the ζ phase and the base steel sheet is most preferably 0%.

When the major axis of the oxides including Si and/or Mn is 0.2 μm ormore, cracking started from the oxides becomes remarkable and when themajor axis of the oxides is less than 0.2 μm, the oxides hardly work asan origin of cracking. This is because a degree of stress concentrationvaries depending on the size of the oxide at the time of deformation ofthe hot-dip galvanized steel sheet. Specifically, as the size of theoxides increases (the major axis becomes longer), stress is more easilyconcentrated at the time of deformation and the plated layer is moreeasily peeled off.

In addition, the hot-dip galvanized layer may include a δ1 phase(FeZn₇). However, in order to increase the fraction of the δ1 phase, thebase steel sheet is required to be heated to alloy the plated layerafter the base steel sheet is immersed in the plating bath, and thetensile properties of the base steel sheet are deteriorated due toheating. From this view point, it is preferable that the fraction of theδ1 phase is small. Particularly, the ratio of the interface of the δ1phase in contact with the base steel sheet is preferably 20% or less inthe entire interface between the plated layer and the base steel sheet.

The ratio of the interface between the ζ phase and the base steel sheetwith respect to the entire interface between the plated layer and thebase steel sheet in the embodiment can be obtained as follows.

That is, a thickness cross section parallel to the rolling direction ofthe base steel sheet is set as an observed section and a sample iscollected. The observed section is subjected to mirror polishing andobservation is performed until the total length L of the observedinterfaces between the plated layer and the base steel sheet reaches 200μm or more by using a field emission scanning electron microscope(FE-SEM). In the same visual field as the visual field in which L isobserved, grains having a columnar shape are considered to be the ζphase or the δ1 phase and the total length L1 of the interfaces betweenthe ζ phase and the δ1 phase and the base steel sheet is measured.Subsequently, in the same visual field as the visual field in which L1is observed, high resolution crystal orientation analysis is performedaccording to EBSD (Electron Bach-scattering Diffraction) method using aFE-SEM to identify the δ1 phase. Thus, the total length L2 of theinterfaces between the δ1 phase and the base steel sheet is obtained.(L1−L2)/L is considered as the ratio of the interface between the ζphase and the base steel sheet in the entire interface between theplated layer and the base steel sheet.

In the same manner, L2/L is considered as the ratio of the interfacebetween the δ1 phase and the base steel sheet in the entire interfacebetween the plated layer and the base steel sheet.

The ζ phase and the δ1 phase may be identified according to methodsother than the above EBSD method. For example, the ζ phase and the δ1phase may be determined based on a difference in amount of Zn by mappingthe Zn element in the plated layer using a field emission electron probemicro analyzer (FE-EPMA).

In order to make the ζ phase appear to be clear, the observed sectionmay be corroded using a corrosive liquid such as nital after the sampleis subjected to mirror polishing.

The presence of the coarse oxides having the major axis of 0.2 μm ormore is, by the above method of performing the cross section SEMobservation, determined by observing major axes of photographed oxides.

The oxide-containing ζ grains are determined by a difference of tones,in observing a SEM backscattered electron (BSE) image of an interfacealloy layer. Since a number of backscattered electron images increaseswith an atomic number of an atom, oxides appear to be darker than thesurroundings. A position which an oxide is formed is depending on anannealing dew point, it is formed inside of a surface layer of a steelsheet not on a surface of the steel sheet when the dew point is higher(about 0° C. or more). After a plated layer is formed, alloying proceedbetween the plated layer and a base steel sheet, when Fe in the surfacelayer of the base steel sheet diffuse into the plated layer, oxides areabsorbed to the plated layer from the surface layer to insidesequentially. In addition, the major axes of each of the determinedoxides in the observed section are measured, and oxides having the majoraxis of 2 μm or more is determined as coarse oxides.

[Plated Amount of Hot-Dip Galvanizing: 10 to 100 g/m²]

Since sufficient corrosion resistance is not obtained when a platedamount on one surface of the base steel sheet in the hot-dip galvanizedlayer is small, it is preferable that the plated amount of the hot-dipgalvanized layer on one surface of the base steel sheet is 10 g/m² ormore. From the viewpoint of corrosion resistance, the plated amount ismore preferably 20 g/m² or more and even more preferably 30 g/m² ormore. On the other hand, when the plated amount of the plated layer islarge, the wear of electrodes is significant at the time of performingspot welding, and reduction in a weld nugget diameter or deteriorationin welded joint strength at the time of continuously performing spotwelding occur. Therefore, the plated amount of the plated layer is 100g/m² or less. From the viewpoint of continuous weldability, the platedamount is more preferably 93 g/m² or less and even more preferably 85g/m² or less.

(Method of Producing Hot-Dip Galvanized Steel Sheet)

Next, the method of producing the hot-dip galvanized steel sheetaccording to the embodiment will be described in detail.

The method of producing the hot-dip galvanized plated steel sheetaccording to the embodiment includes a hot rolling step which is a stepof performing a hot rolling with heating the slab including the abovechemical compositions 1,080° C. or higher and setting a rollingcompletion temperature to be in a range of 850 to 980° C. to make a hotrolled steel sheet and coiling as a coil, and which is a step ofcontrolling a temperature of the hot rolled steel sheet step to satisfythe Expression (1), which will be described later, in a cooling stepafter the hot rolling step until 300° C., after a pickling after the hotrolling step, a cold rolling step of performing a cold rolling with atotal rolling reduction of 85% or less, an annealing step includingheating at an average heating rate of 1.0° C./second or more in a rangeof 600° C. to 750° C. and with a maximum heating temperature in a rangeof (Ac1+25°)° C. or more and Ac3° C. or less, and 750° C. or more, andcooling at an average cooling rate of 0.1 to 5.0° C./second in a rangeof 760° C. to 700° C. and an average cooling rate of 1.0° C./second ormore in a range of 650° C. to 500° C., after the annealing step, aplating step which is a step of hot-dip galvanizing the steel sheetsurface by immersing the steel sheet in a plating bath under the platingconditions of a steel sheet temperature of 440° C. to 480° C. and anamount of effective Al of 0.050% to 0.180% by mass in the plating bathwhen the steel sheet enters the plating bath having a plating bathtemperature of 450° C. to 470° C., to form a plated layer, and after theplating step, a cooling step of cooling the steel sheet to 350° C.satisfying the Expression (2) which will be described later and aprocessing step of performing a bending-bending back deformation twiceor more in total using a roll with a diameter of 50 mm to 800 mm afterthe steel sheet is further cooled to 100° C. or less.

Hereinafter, each production step will be described in detail.

In order to produce the hot-dip galvanized steel sheet according to theembodiment of the present invention, first, a base steel sheet isproduced.

In order to produce the base steel sheet, a slab including the abovechemical components (composition) is casted.

For the slab to be supplied to hot rolling, a continuous casting slab ora slab produced by a thin slab caster or the like can be used.

[Hot Rolling Step]

In the hot rolling step, in order to suppress anisotropy of crystalorientation caused by casting, the heating temperature of the slab ispreferably 1,080° C. or higher. The heating temperature of the slab ismore preferably 1,150° C. or higher. On the other hand, the upper limitof the heating temperature of the slab is not particularly limited. Inorder to heat the slab at higher than 1,300° C., a large amount ofenergy needs to be applied, which causes a significant increase in theproduction cost. Thus, the heating temperature of the slab is preferably1,300° C. or lower.

After heating the slab, hot rolling is performed. When the temperaturewhen the hot rolling is completed (rolling completion temperature) islower than 850° C., the rolling reaction force is high and thus it isdifficult to stably obtain a predetermined thickness. Therefore, thetemperature when the hot rolling is completed is preferably 850° C. orhigher and more preferably 870° C. or higher. On the other hand, inorder to set the temperature when the hot rolling is completed to behigher than 980° C., in the step from the completion of heating of theslab to the completion of hot rolling, a device for heating the steelsheet is necessary and a high cost is required. Therefore, thetemperature when the hot rolling is completed is 980° C. or lower andmore preferably 950° C. or lower.

Next, the hot-rolled steel sheet which has been subjected to hot rollingis coiled as a coil. The average cooling rate in the cooling processfrom the hot rolling to the coiling is preferably 10° C./second or more.This is because when transformation proceeds at a lower temperature, thegrain size of the hot-rolled steel sheet is made fine and the effectivegrain size of the base steel sheet after cold rolling and annealing ismade fine.

The coiling temperature of the hot-rolled steel sheet is preferably 450°C. or higher and 650° C. or lower. This is because in the microstructureof the hot-rolled steel sheet, pearlite and/or coarse cementite having amajor axis of 1 μm or more is formed in a dispersed manner, strainintroduced by cold rolling is localized. And reverse transformation toaustenite having various crystal orientations occurs in the annealingstep. Thus, the effective crystal orientation of the base steel sheetafter annealing can be refined. When the coiling temperature is lowerthan 450° C., pearlite and/or coarse cementite may not be formed andthus this case is not preferable. On the other hand, when the coilingtemperature is higher than 650° C., pearlite and ferrite are formed in abelt shape long in the rolling direction, and effective grains of thebase steel sheet generated from the ferrite part after cold rolling andannealing tend to extend in the rolling direction and be coarse, whichis not preferable.

Here, in the surface of the base steel sheet after an annealing, inorder to control a hard structure to be in a predetermined volumefraction, in the hot rolling step, it is necessary to decarburizeappropriately from the surface of the base steel sheet. Decarburizationbehavior may be controlled by an atmosphere control, however, itrequires a large scale facility and a large burden of cost. For thisreason, in the embodiment, decarburization behavior is controlled bycontrolling a cooling rate and a temperature of the steel sheet, in asection from a completion of a finishing rolling (rolling completion) to300° C.

Temperature control of the base steel sheet is performed in arrange inwhich the temperatures is Ae 3* or less which is a temperature at whichBCC phase of Fe at the surface of the case steel sheet is stable, in asection from the completion of a finishing rolling to 300° C. This isbecause, decarburization from BCC phase of Fe proceeds faster comparingto FCC phase which is a stable phase in a high temperature. In theembodiment, when the temperature of the base steel sheet is in atemperature range lower than 300° C., diffusion speeds of oxides aresufficiently slow, it can be considered that a decarburizationproceeding speed does not influence the decarburization behavior, atemperature range of the temperature control of the base steel sheet inthe hot rolling step is a section from the completion of a finishingrolling to 300° C.

Ae 3* can be obtained by the following formula.

Ae 3* [° C.]=885+31.7Si−29.3Mn+123.2Al−18.2Cr−40.0Ni−21.0Cu+12.6Mo

In the above formula, C, Si, Mn, Al, Cr, Ni, Cu, and Mo respectivelyrepresent an addition amount [% by mass] thereof.

Further, the decarburization behavior of the steel sheet is controlledin a first period from the completion of the finishing rolling to thecoiling on a coil and a second period after the coiling to reaching tothe room temperature respectively. This is because, a decarburizationproceeds in the atmosphere in the first period, a decarburization in thesecond period proceeds in a condition that the coiled steel sheetscontact and outer air does not intrude, decarburization speeds greatlyvary in these terms.

Specifically, in order to decarburize the surface layer of the steelsheet appropriately, the temperature of the steel sheet is controlled tobe in a range satisfying the following Expression (1) in the coolingstep from the completion of the finishing rolling to 300° C. TheExpression (1) is an expression related to a degree of progress of thedecarburization behavior, the larger value of the Expression (1)indicates the decarburization proceeds.

In the Expression (1), t [second] represents the time elapsed from thecompletion of the finishing rolling, t1 [second] represents the timeelapsed from the completion of the finishing rolling to the Ae 3*temperature, t2 [second] represents the time elapsed from the completionof the finishing rolling to the coiling, t3 [second] represents the timeelapsed from the completion of the finishing rolling until the steelsheet temperature reaches 300° C. T (t) [° C.] represents a steel sheettemperature, W_(Si) [% by mass] and W_(Mn) [% by mass] respectivelyrepresent average amounts of each atom of Si and Mn in the entire steelsheet. Further, α, β, γ, δ are constant terms, and are 8.35×10,2.20×10⁴, 1.73×10¹⁰, 2.64×10⁴ respectively.

$\begin{matrix}{0.8 \leq \begin{bmatrix}{{\int_{t\; 1}^{t\; 2}{\alpha \cdot {\exp\left( {- \frac{\beta}{{T(t)} + 273}} \right)} \cdot {tdt}}} +} \\{\int_{t\; 2}^{t\; 3}{\gamma \cdot W_{Si}^{2.5} \cdot W_{Mn}^{0.5} \cdot {\exp\left( {- \frac{\delta}{{T(t)} + 273}} \right)} \cdot {tdt}}}\end{bmatrix}^{0.5} \leq 20.0} & {{Expression}\mspace{14mu}(1)}\end{matrix}$

In the above Expression (1), the first integral term in the brackets isa term related to the degree of progress of decarburization duringcooling in the first period, and the second integral term in thebrackets is a term related to the degree of progress of decarburizationduring cooling in the second period. In any of the term, decarburizationproceeds as the temperature of the base steel sheet is high and aretaining time is long. Particularly in the second period, since oxygenwhich is an element for promoting decarburization hardly exists in theatmosphere and decarburization proceeds by oxygen which is attracted bySi and Mn in a steel from a surface layer of a scale layer, the secondintegral term includes the influence of the amounts of Si and Mn, andthe value of the Expression (1) increases as the amounts of Si and Mn inthe steel increases, indicating that decarburization proceeds.

In the cooling step after the completion of finish rolling, when thevalue of the above Expression (1) is less than 0.8, the surface layer ofthe base steel sheet is hardly decarburized, and V1/V2 which is theratio of the volume fraction V1 of the hard structure in the surfacepart and the volume fraction V2 of the hard structure centered at theposition of ¼ thickness from the surface of the base steel sheet is morethan 0.90 and the flexibility deteriorates, therefore cooling isperformed so that the value of the above Expression (1) is 0.8 or more.From this viewpoint, it is preferable to perform cooling so that thevalue of the above Expression (1) is 1.0 or more, more preferably 1.3 ormore. On the other hand, when the value of the above Expression (1) ismore than 20.0, the surface layer part of the steel sheet is excessivelydecarburized, V1/V2 becomes less than 0.30, and the fatigue resistanceof the steel sheet significantly deteriorates, therefore cooling isperformed so that the value of the above Expression (1) is 20.0 or less.From this viewpoint, it is preferable to perform cooling so that thevalue of the above Expression (1) is 15.0 or less, more preferably 10.0or less.

Next, pickling of the hot-rolled steel sheet produced in theabove-described manner is performed. The pickling is performed forremoving oxides on the surface of the hot-rolled steel sheet. Thus, thepickling is important to improve plating adhesion of the base steelsheet. The pickling may be performed at once or a plurality of timesseparately.

[Cold Rolling Step]

Next, the hot-rolled steel sheet after pickling is subjected to coldrolling to obtain a cold-rolled steel sheet.

In the cold rolling, when the total rolling reduction is more than 85%,the ductility of the base steel sheet is impaired and a risk of breakingof the base steel sheet during the cold rolling becomes higher.Therefore, the total rolling reduction is 85% or less. From thisviewpoint, the total rolling reduction is preferably 75% or less andmore preferably 70% or less. The lower limit of the total rollingreduction in the cold rolling step is not particularly limited. When thetotal rolling reduction is less than 0.05%, the shape of the base steelsheet is not uniform and plating adheres unevenly, so that an externalappearance of the steel sheet is impaired. Therefore, the total rollingreduction is preferably 0.05% or more and more preferably 0.10% or more.The cold rolling is preferably performed in a plurality of passes, butany number of passes of the cold rolling and any rolling reductiondistribution to each pass are applicable.

When the total rolling reduction in the cold rolling is within a rangeof more than 10% and less than 20%, recrystallization does not progresssufficiently in the following annealing step. Therefore, coarse grainsin which malleability is lost by including a large amount ofdislocations remain near the surface, and bendability and fatigueresistance properties of the hot-dip galvanized steel sheet may bedeteriorated in some cases. In order to avoid this, it is effective tomake malleability remain by reducing the total rolling reduction andreducing accumulation of dislocations to the grains. Alternatively, itis also effective to turn the processed structure into recrystallizedgrains having a small amount of accumulation of dislocations inside byreducing the total rolling reduction and making recrystallizationsufficiently proceed in the annealing step. From the viewpoint ofreducing the accumulation of dislocations to the grains, the totalrolling reduction in the cold rolling is preferably 10% or less and morepreferably 5.0% or less. On the other hand, in order to makerecrystallization sufficiently proceed in the annealing step, the totalrolling reduction is preferably 20% or more and more preferably 30% ormore.

[Annealing Step]

In the embodiment of the present invention, the cold-rolled steel sheetis subjected to annealing. In the embodiment of the present invention, acontinuous annealing and plating line having a preheating zone, areduction zone, and a plating zone is used. While performing theannealing process, the steel sheet is allowed to pass though thepreheating zone and the reduction zone and before the steel sheetreaches the plating zone, the annealing step is completed. Then, theplating step is preferably performed in the plating zone.

As described above, in the case of using a continuous annealing andplating line in the annealing step and the plating step, for example,the method described below is preferably used.

First, the steel sheet is allowed to pass through the preheating zone inwhich the air ratio in the mixed gas of air and fuel gas used for apreheating burner is 0.7 to 1.2, while heating the steel sheet to asteel sheet temperature of 400° C. to 800° C.

By the above step, oxides are formed at the steel sheet surface part.Here, it is a ratio between the volume of air included in the mixed gasper unit volume and the volume of air which is theoretically required tocause complete combustion of fuel gas contained in the mixed gas perunit volume. Next, by heating the steel sheet to 750° C. or more in thepreheating zone in which a ratio between H₂O and H₂ isP(H₂O)/P(H₂):0.0001 to 2.0, it can be a step of performing cooling aftera reduction of oxides formed in the preheating zone. And then, a platingstep after the annealing step can be a step of performing a hot-dipgalvanizing a steel sheet in a condition of immersing the steel sheet ina plating bath under conditions of a plating bath temperature of 450° C.to 470° C., a steel sheet temperature of 440° C. to 480° C. when thesteel sheet enters the plating bath, and an amount of effective Al of0.05% to 0.18% by mass in the plating bath.

The heating rate in the annealing step is related to the progress ofdecarburization in the steel sheet surface part through the treatmenttime in the preheating zone. When the heating rate is low, the steelsheet is exposed to an oxidation atmosphere for a long period of timeand thus decarburization proceeds. Particularly, the heating rate at600° C. to 750° C. is important, in order to secure the treatment timein the preheating zone to promote ζ phase formation, the average heatingrate is preferably 10° C./second or less. On the other hand, when theheating rate at 600° C. to 750° C. is too slow, oxidation excessivelyproceeds and coarse oxides are formed inside the steel sheet in somecases. To avoid formation of coarse oxides inside the steel sheet, theaverage heating rate is 1.0° C./second or more at the temperature range.

In the preheating zone, the steel sheet surface part is subjected to anoxidation treatment for forming a Fe oxide coating film having anappropriate thickness. At this time, the steel sheet is allowed to passthrough the preheating zone in which the air ratio in the mixed gas ofair and fuel gas used for a preheating burner, which will be describedbelow, is 0.7 or more, while heating the steel sheet to a steel sheettemperature of 400° C. to 800° C.

The term “air ratio” is a ratio between “the volume of air included inthe mixed gas per unit volume” and “the volume of air which istheoretically required to cause complete combustion of fuel gascontained in the mixed gas per unit volume”, and is represented by thefollowing expression.“Air ratio”=[volume of air included in the mixed gas per unit volume(m³)]/[volume of air which is theoretically required to cause completecombustion of fuel gas contained in the mixed gas per unit volume(m³))]}

In the embodiment, the base steel sheet which is allowed to pass throughthe preheating zone is heated under the above conditions to form a Feoxide coating film (oxide) having a thickness of 0.01 to 5.0 μm on thesurface layer of the base steel sheet. The Fe oxide coating film (oxide)formed on the steel sheet surface is reduced in the reduction zone andbecomes a surface excellent in plating adhesion.

In the case in which the air ratio is more than 1.2 and too large in thesteel sheet surface part, excessive Fe oxide coating film is formed onthe steel sheet surface part and after reduction, the decarburized layerbecomes excessively thick. The oxide coating film is reduced in thereduction zone and becomes a surface excellent in plating adhesion.However, in the case in which air ratio is less than 0.7 and is toosmall, a predetermined oxide cannot be obtained.

When the steel sheet temperature for allowing the steel sheet to passthrough the preheating zone is lower than 400° C., a sufficient oxidefilm cannot be formed. On the other hand, when the steel sheettemperature for allowing the steel sheet to pass through the preheatingzone is a high temperature of higher than 800° C., the oxide coatingfilm excessively grows up and it will be difficult to set a thickness ofthe decarburized layer within a predetermined range Accordingly, thesteel sheet temperature for allowing the steel sheet to pass through thepreheating zone is 800° C. or lower and more preferably 750° C. orlower.

The maximum heating temperature in the annealing step is an importantfactor for controlling the fraction of the microstructure related to theformability of the steel sheet to be within a predetermined range. Whenthe maximum heating temperature is low, a large amount of coarseiron-based carbides is left unmelted in the steel and thus formabilityis deteriorated. When the maximum heating temperature is lower than 750°C., the coarse iron-based carbides in a hot rolled steel sheet are notsufficiently melted and remain in a product sheet and there is a concernof ductility being impaired. In order to sufficiently solid-dissolve theiron-based carbides to enhance formability, the maximum heatingtemperature is (Ac1 point+25°)° C. or higher and 750° C. or higher, andthe maximum heating temperature is preferably (Ac1 point+50°)° C. orhigher. On the other hand, a ferrite fraction in steel significantlydecreases when the maximum heating temperature is more than Ac3 point,the maximum heating temperature is Ac3 point or less. Further, from theviewpoint of plating adhesion, it is preferable that the maximum heatingtemperature is lower for reducing oxides on the surface of the basesteel. From this viewpoint, the maximum heating temperature ispreferably 850° C. or lower and more preferably 830° C. or lower.

The Ac1 point and Ac3 point of the steel sheet are a starting point anda completion point of austenite reverse transformation. Specifically,the Ac1 point and Ac3 point are obtained by cutting off a small piecefrom the steel sheet after hot rolling, heating the piece to 1,200° C.at 10° C./second, and measuring the amount of volume expansion duringheating.

The temperature preferably reaches the maximum heating temperature inthe annealing step (750° C. or higher) in the reduction zone. In thereduction zone, the thin Fe oxide coating film formed on the steel sheetsurface in the preheating zone is reduced to enhance plating adhesion.Therefore, a ratio between a water vapor partial pressure P(H₂O) and ahydrogen partial pressure P(H₂), P(H₂O)/P(H₂), in the atmosphere in thereduction zone is 0.0001 to 2.00. When P(H₂O)/P(H₂) is less than 0.0001,Si and/or Mn oxides which act as a plating peeling origin are formed onthe outermost layer. On the other hand, when the P(H₂O)/P(H₂) is morethan 2.00, refinement excessively proceeds in the steel sheet surfaceand alloying of the plated layer excessively proceeds. Thus, platingadhesion is deteriorated. Further, when the P(H₂O)/P(H₂) is more than3.00, decarburization excessively proceeds and a hard phase of the basesteel sheet surface is remarkably reduced. From this viewpoint,P(H₂O)/P(H₂) is more preferably within a range of 0.002 to 1.50 and morepreferably within a range of 0.005 to 1.20.

As described above, when P(H₂O)/P(H₂) is 0.0001 to 2.00, in a case thatwater vapor is added into a reduction atmosphere, Si and/or Mn oxideswhich act as a plating peeling origin are not formed on the outermostlayer, and Si and Mn form fine oxides inside the steel sheet surfacealternatively. A size of the fine oxides is 0.01 μm or more and 0.4 μmor less in the above condition. In addition, water vapor in thereduction atmosphere causes the base steel surface to be decarburizedand thus the base steel surface is turned into ferrite. Since theseSi—Mn inside oxides suppress the growth of Fe recrystallization during areduction annealing, on the surface of the base steel, a refined layerhaving an average thickness of 0.1 μm or more and 5 μm or less andhaving a ferrite having an average grain size of 0.1 μm or more and 3 μmor less is formed.

In the annealing step, at a cooling step before the plating step afterthe temperature reaches the maximum heating temperature and before thesteel sheet reaches a plating bath (cooling step before plating), apredetermined microstructure is obtained by controlling a temperature ofa steel sheet in two steps of a temperature range of 760° C. to 700° C.and a temperature range of 650° C. to 500° C. First, in order tosufficiently promote a formation of ferrite, an average cooling rate ina range of 760° C. to 700° C. is defined. In some cases, formation offerrite may not be sufficiently proceeded when the average cooling ratein the range of 760° C. to 700° C. is more than 5.0° C./second, theaverage cooling rate is 5.0° C./second or less. In order to promote aformation of ferrite, the average cooling rate is preferably 3.5°C./second or less and more preferably 2.5° C./second or less. In somecases, excessive pearlite may be formed when the average cooling rate inthe range of 760° C. to 700° C. is less than 0.3° C./second, the averagecooling rate is 0.3° C./second or more. In order to avoid a formation ofpearlite, the average cooling rate is preferably 0.5° C./second or moreand more preferably 0.7° C./second or more.

Next, in order to avoid a formation of excessive pearlite and/or coarsecementite, an average cooling rate in a range of 650° C. to 500° C. isdefined. When the average cooling rate in the range of 650° C. to 500°C. is less than 1.0° C./second, pearlite and/or coarse cementite isformed greatly, the average cooling rate is 1.0° C./second or more.Since it is preferable that pearlite and/or coarse cementite is notincluded in a steel, in order to avoid a formation of these structuressufficiently, the average cooling rate is preferably 2.0° C./second ormore and more preferably 3.0° C./second or more. Although the upperlimit of the average cooling rate in a range of 650° C. to 500° C. isnot particularly provided, an excessively high average cooling rate isnot preferable since a special cooling facility and a coolant which doesnot interfere with the plating step are required to obtain theexcessively high average cooling rate. From this viewpoint, the averagecooling rate in the above-described temperature range is preferably 100°C./second or less and more preferably 70° C./second or less.

Subsequent to the cooling step before plating, in order to obtaintempered martensite, in a period after the steel sheet temperaturereaches 500° C. and before the steel sheet reaches a plating bath, as amartensitic transformation treatment, the steel sheet may be retained ina predetermined temperature range for a predetermined period of time.Regarding the martensitic transformation treatment temperature, amartensitic transformation starting temperature Ms point is set as anupper limit and the lower limit of the martensitic transformationtreatment temperature is 50° C. In addition, the martensitictransformation treatment time is 1 second to 100 seconds. The martensiteobtained in the treatment enters a plating bath at a high temperature inthe plating step and then is changed into tempered martensite.

The Ms point is calculated by the following expression.Ms Point [° C.]=541−474C/(1−VF)−15Si−35Mn−17Cr−17Ni+19Al

In the above expression, VF represents the volume fraction of ferrite,and each of C, Si, Mn, Cr, Ni, and Al represents the amount [% by mass]of each element added.

It is difficult to directly measure the volume fraction of ferriteduring production. Therefore, when the Ms point is determined in theembodiment, a small piece is cut off from the cold-rolled steel sheetbefore the steel sheet is allowed to pass through the continuousannealing and plating line. The small piece is annealed at the sametemperature as in the case in which the small piece is allowed to passthrough the continuous annealing and plating line and a change in thevolume of the ferrite of the small piece is measured so that a numericalvalue calculated using the result is used as the volume fraction VF ofthe ferrite.

Further, in order to promote the formation of bainite, in a period afterthe steel sheet temperature reaches 500° C. and before the steel sheetreaches a plating bath, the steel sheet may be retained at apredetermined temperature range for a predetermined period of time as abainitic transformation treatment.

When the bainitic transformation treatment temperature is more than 500°C., a formation of pearlite and/or coarse cementite proceed. Therefore,the bainitic transformation treatment temperature is 500° C. or lower.When the bainitic transformation treatment temperature is lower than350° C., the transformation is not promoted. Therefore, the bainitictransformation treatment temperature is 350° C. or higher. The bainitictransformation treatment time is 10 seconds or more, in order to promotethe transformation sufficiently. The bainitic transformation treatmenttime is 500 seconds or less, in order to suppress formation of pearliteand/or coarse cementite.

After the cooling step before plating, in the case in which both thebainitic transformation treatment and the martensitic transformationtreatment are performed, regarding the treatment order, the martensitictransformation treatment and the bainitic transformation treatment areperformed.

[Plating Step]

Next, the base steel sheet obtained as described above is immersed in aplating bath.

The plating bath mainly includes zinc and has a composition in which theamount of effective Al, which is a value obtained by subtracting thetotal amount of Fe from the total amount of Al in the plating bath, is0.050 to 0.180% by mass. When the amount of effective al in the platingbath is less than 0.050%, the entering of Fe into the plated layerexcessively proceeds to impair plating adhesion. Thus, it is requiredthat the amount of effective Al is 0.050% or more. From this viewpoint,the amount of effective Al in the plating bath is preferably 0.065% ormore and more preferably 0.070% or more. On the other hand, when theamount of effective Al in the plating bath is more than 0.180%, Al-basedoxides are formed at the boundary between the base steel sheet and theplated layer and the movement of Fe and Zn atoms is inhibited at thesame boundary. Thus, ζ phase formation is suppressed and platingadhesion is significantly deteriorated. From this viewpoint, it isrequired that the amount of effective Al in the plating bath is 0.180%or less and the amount of effective Al is preferably 0.150% or less andmore preferably 0.135% or less.

One or two or more elements of Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu,Ge, Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Rb, Sb, Si, Sn, Sr,Ta, Ti, V, W, Zr, and REM may be mixed in the plating bath and there isa preferable case in which the corrosion resistance or workability ofthe hot-dip galvanized layer is improved according to the content ofeach element in the plating bath or the like.

In addition, the temperature of the plating bath is 450° C. to 470° C.When the temperature of the plating bath is lower than 450° C., theviscosity of the plating bath is excessively increased and thus it isdifficult to control the thickness of the plated layer so that theexternal appearance of the hot-dip galvanized steel sheet is impaired.On the other hand, when the temperature of the plating bath is higherthan 470° C., a large amount of fumes is generated, and it is difficultto realize safe production, so that the temperature of the plating bathis 470° C. or lower.

In addition, the steel sheet temperature when the steel sheet enters theplating bath is lower than 440° C., it is required to give a largequantity of heat to the plating bath to stabilize the temperature of theplating bath at 450° C. or higher, which is practically inappropriate.On the other hand, when the steel sheet temperature when the steel sheetenters in the plating bath is higher than 480° C., it is required tointroduce a facility of removing a large quantity of heat from theplating bath to stabilize the temperature of the plating bath at 470° C.or lower, which is inappropriate in terms of production costs.Accordingly, in order to stabilize the temperature of the plating bath,the temperature of the base steel sheet when the base steel sheet entersthe plating bath is preferably 440° C. or higher and 480° C. or lower.In addition, in order to control a ζ phase formation behavior to beappropriate, it is more preferable that the temperature when the basesteel sheet enters the plating bath is controlled to 450° C. or higherand 470° C. or lower.

When the bath temperature of the plating bath is within a range of 450to 470° C., the embodiment can be carried out. However, when the bathtemperature is not stabilized within a range of 450 to 470° C., the ζphase in the plating bath becomes not uniform, which causesnon-uniformity in the external appearance and adhesion of the platedlayer. Therefore, in an actual production, the bath temperature ispreferably any value in a range of 450 to 470° C. and is constant.Therefore, it is preferable that the entering temperature is coincidentwith the bath temperature. However, due to the limit of controllabilityof an actual production facility, the entering temperature is preferablyin a range of the bath temperature of the plating bath ±4° C.

Depending on the production line of the hot-dip galvanized steel sheet,there is a case that a device necessary for performing the “cooling stepafter plating” to be described later is not provided and themanufacturing conditions of the embodiment can not be performed in somecases. In that case, by appropriately controlling the immersion time ofthe plating bath, it is possible to manufacture the same product as inthe embodiment. In other words, if the immersion time of the steel sheetin the plating bath is extended, it is possible to form the ζ phase atthe interface between the plating layer and the base steel sheet as inthe case of performing the “cooling step after plating”.

The necessary immersion time depends on the amount of Al in the platingbath, however, it is necessary that the immersion time is 3 seconds ormore. It is preferable that the immersion time is 5 seconds or more, andis more preferably 10 seconds or more, even more preferably 20 secondsor more.

In order to have an appropriate plated amount after immersing the steelsheet in the plating bath, an excessive amount of zinc on the surface ispreferably removed by blowing a high pressure gas mainly includingnitrogen onto the steel sheet surface.

[Cooling Step after Plating]

After the steel sheet is immersed in a plating bath, in the cooling stepof cooling to room temperature after plating, by controlling a coolingtreatment so that it satisfies the following Expression (2), anappropriate amount of ζ phase is obtained in the plated layer.

T(t) [° C.] represents a steel sheet temperature, t[second] representsthe time elapsed from the time point when the steel sheet is taken outfrom the plating bath as a starting point, t4[second] represents thetime elapsed from the time point when the steel sheet is taken out fromthe plating bath as a starting point and until the steel sheettemperature reaches 350° C., and W*_(AI) [% by mass] represents theamount of effective Al in the plating bath. In addition, ε, θ, and μeach represents constant terms, each of which is 2.62×10⁷, 9.13×10³, and1.0×10⁻¹.

$\begin{matrix}{0.40 \leq \left\lbrack {\int_{t\; 0}^{t\; 4}{{ɛ \cdot \exp}{\left\{ {- \frac{\theta \cdot \left( \frac{W_{A\; 1}^{*}}{\mu} \right)^{0.2}}{T(t)}} \right\} \cdot {tdt}}}} \right\rbrack^{0.5} \leq 2.20} & {{Expression}\mspace{14mu}(2)}\end{matrix}$

The above Expression (2) is an expression related to a ζ phase formationbehavior and as the value of the above Expression (2) increases, ζ phaseformation proceeds in the plated layer. As the steel sheet temperatureincreases and the treatment time increases, the value of the aboveExpression (2) increases. In addition, when the amount of effective Alin the plated layer is increased, the value of the above Expression (2)is decreased and ζ phase formation is inhibited. When the steel sheettemperature is within a temperature range of 350° C. or lower, thediffusion of Fe atoms from the base steel sheet to the plated layerhardly occur and ζ phase formation is nearly stopped. Therefore, theabove Expression (2) is used for calculation at a steel sheettemperature within a range of 350° C. or higher.

In the cooling step after plating which is performed after the immersingthe steel sheet in the plating bath, when the value of the aboveExpression (2) is less than 0.40, a sufficient amount of the ζ phase isnot obtained in the plated layer and plating adhesion is impaired.Therefore, it is necessary to control the cooling treatment so that thevalue of Expression (2) is 0.40 or more. When the value of the aboveExpression (2) is 0.40 or more, ζ phase formation is sufficientlypromoted and the ratio ((A*/A)×100) of the interface (A*) between the ζphase and the base steel sheet in the entire interface (A) between thehot-dip galvanized layer and the base steel sheet is 20% or more. Inaddition, when the value of the above Expression (2) is 0.40 or more,the ratio ((A**/A*)×100) of the interface (A**) formed between the ζgrains in which coarse oxides are present and the base steel sheet inthe interface (A*) between the ζ phase and the base steel sheet is 50%or less.

In order to further enhance plating adhesion, it is preferable that thecooling treatment is controlled such that the value of the aboveExpression (2) is 0.50 or more, and it is more preferable that thecooling treatment is controlled such that the value of the aboveExpression (2) is 0.60 or more. On the other hand, when the value of theabove Expression (2) in the cooling treatment is excessively large,alloying of the plated layer proceeds and the Fe content in the platedlayer is excessively increased. Thus, plating adhesion is impaired. Fromthe viewpoint, it is required that the cooling treatment is performedsuch that the value of the above Expression (2) is 2.20 or less. Inorder to further enhance plating adhesion, it is preferable that thecooling treatment is controlled such that the value of the aboveExpression (2) is 2.00 or less and it is more preferable that thecooling treatment is controlled such that the value of the aboveExpression (2) is 1.80 or less.

Here, when the temperature of the steel sheet is increased after thesteel sheet is taken out from the plating bath, the value of the aboveExpression (2) is significantly increased and plating adhesion isdeteriorated. In addition, the microstructure of the steel sheet isreformed and predetermined hard structure cannot be obtained andstrength deteriorates. Further, coarse carbides are formed and there isa concern of deterioration in formability of the hot-dip galvanizedsteel sheet. Therefore, the steel sheet temperature after the steelsheet is taken out from the plating bath is not allowed to be higherthan the higher temperature of the steel sheet temperature before thesteel sheet is immersed in the plating bath and the plating bathtemperature.

On the other, as shown in a general method of producing a hot-dipgalvanized steel sheet, when the steel sheet is rapidly cooled after thesteel sheet is immersed in the plating bath, the value of the aboveExpression (2) is significantly decreased. As a result, a sufficientamount of the ζ phase is not obtained and plating adhesion isdeteriorated. In order to set the value of the above Expression (2) tobe within a predetermined range, for example, after the steel sheet istaken out from the plating bath, the steel sheet may be subjected to anisothermal retention treatment for a predetermined period of time andthen rapidly cooled.

In addition, as long as the value of the above Expression (2) is set tobe within a predetermined range, another optional temperature controlmay be performed. That is, as long as the temperature control forsetting the value of the above Expression (2) to be within the range ofthe embodiment, any cooling control form may be adopted. For example, acooling form of rapidly cooling after an isothermal retention treatmentmay be used or a cooling form of almost constant slow cooling may beused.

By the above cooling treatment which satisfies the Expression (2),cooling at an average cooling rate of 1.0° C./second or more to 250° C.or lower may be performed after a sufficient amount of the ζ phase isobtained in the plated layer, in order to obtain the hard structure. Inorder to obtain a fresh martensite phase and a tempered martensitephase, the average cooling rate is preferably 3.0° C./second or more andmore preferably 5.0° C./second or more.

Further, a reheating treatment may be performed in order to obtaintempered martensite after the steel sheet is cooled to 250° C. or lower.The treatment temperature and the treatment time of the reheatingtreatment may be appropriately selected according to desired properties.However, a sufficient effect cannot be obtained at a reheating treatmenttemperature of lower than 250° C. On the other hand, when the reheatingtreatment temperature is higher than 350° C., the plated layer changesin quality, and there is a concern that plating adhesion deteriorates.Therefore, the reheating treatment temperature is preferably 250° C. orhigher and 350° C. or lower. In addition, when the treatment time of thereheating treatment is longer than 1,000 seconds, the effect of thetreatment is saturated and thus the treatment time is preferably 1,000seconds or shorter.

A bainitic transformation treatment in which the steel sheet is retainedfor 500 seconds or shorter within a temperature range of 250° C. to 350°C. to obtain residual austenite may be performed after a sufficientamount of the ζ phase is obtained in the plated layer by the coolingtreatment satisfying the above Expression (2). When a treatmenttemperature is lower than 250° C., martensite is formed and a sufficientamount of residual austenite cannot be obtained. On the other hand, whenthe bainitic transformation treatment temperature is higher than 350°C., there is a concern that an excessively large amount of residualaustenite is obtained. Further, when the treatment time is more than 500seconds, coarse carbides are formed from the residual austenite andthere is a concern that formability significantly deteriorates.

After the bainitic transformation treatment (retained for 500 seconds orshorter within a temperature range of 250° C. to 350° C.), in order tofurther stabilize the residual austenite, the steel sheet may be cooledto 250° C. or lower and then a reheating treatment may be performed. Thetreatment temperature and the treatment time of the reheating treatmentmay be appropriately selected according to desired properties. However,a sufficient effect cannot be obtained at a reheating treatmenttemperature of lower than 250° C. When the reheating treatmenttemperature is higher than 350° C., the residual austenite is decomposedand becomes carbides, and there is a concern that the propertiessignificantly deteriorate. Therefore, the treatment temperature ispreferably 350° C. or lower.

In addition, when the treatment time of the reheating treatment islonger than 1,000 seconds, the effect of the treatment is saturated andthus the treatment time is preferably 1,000 seconds or shorter.

[Processing Step]

Next, after the steel sheet is cooled to 100° C. or less, abending-bending back deformation is applied to the plated steel sheet inorder to reduce a residual austenite in the surface layer of the basesteel sheet. The bending can be applied by using a roll with a diameterof 50 mm to 800 mm. When the roll diameter of the roll is less than 50mm, a large amount of strain is introduced in the surface layer of thebase steel sheet by the bending deformation and therefore formability ofthe steel sheet deteriorates. When the roll diameter of the roll is morethan 800 mm, the amount of strain in the surface layer of the base steelsheet is small and therefore the residual austenite is not sufficientlyreduced. Since the bending-bending back deformation reduces the residualaustenite at the surfaces in both sides of the base steel sheet and itis necessary that deformation which each of the sides of the base steelsheet is set as a bending-outward is applied to once or more times onboth sides respectively, therefore it is necessary that thebending-bending back deformation is applied twice or more in total. Bythis step, the residual austenite at the surfaces in both sides of thebase steel sheet can be set within a predetermined range.

The hot-dip galvanized steel sheet according to the embodiment can beproduced by the above-described production method. However, the presentinvention is not limited to the above embodiment. For example, in theembodiment of the present invention, a coating film formed of acomposite oxide including a phosphorus oxide and/or phosphorus may beapplied to the surface of the zinc-plated layer of the hot-dipgalvanized steel sheet obtained by the above-described.

The coating film formed of a composite oxide including a phosphorusoxide and/or phosphorus can function as a lubricant when the steel sheetis worked and can protect the zinc-plated layer formed on the surface ofthe base steel sheet.

Further, in the embodiment of the present invention, cold rolling may beperformed on the hot-dip galvanized steel sheet cooled at roomtemperature at a rolling reduction of 3.00% or less for shapecorrection. The cold rolling may be performed at any stage such asbefore or after the bending-bending back deformation, or in the middleof the bending-bending back deformation.

The method of producing the hot-dip galvanized steel sheet according tothe above-described embodiment of the present invention is preferablyapplied to the production of a hot-dip galvanized steel sheet in whichthe thickness of the base steel sheet is 0.6 mm or more and less than5.0 mm. When the thickness of the base steel sheet is less than 0.6 mm,it is difficult to keep the shape of the base steel sheet flat and thethickness is not appropriate in some cases. In addition, when thethickness of the base steel sheet is 5.0 mm or more, the control ofcooling in the annealing step and the plating step may be difficult.

EXAMPLES

Examples of the present invention will be described below. Theconditions in the examples are just an illustration which is employedfor confirming the feasibility and effects of the present invention. Thepresent invention is not limited to this illustration of conditions. Thepresent invention can employ various conditions so long as not deviatingfrom the gist of the present invention and achieving the object of thepresent invention.

Slabs having the chemical components (composition) A to BY shown inTables 1 to 6 were casted and hot-rolled under the conditions (the slabheating temperature, the rolling completion temperature) shown in Tables7 to 10. Next, the hot-rolled steel sheets were cooled under theconditions (the average cooling rate from hot rolling completion tocoiling, and the coiling temperature, and Expression (1)) shown inTables 7 to 10, and thus hot-rolled steel sheets were obtained.

Thereafter, the hot-rolled steel sheets were subjected to pickling andcold rolling under the condition (rolling reduction) shown in Tables 7to 10 and thus cold-rolled steel sheets were obtained.

Next, the obtained cold-rolled steel sheets were subjected to annealingunder the conditions (the air ratio in the preheating zone, the partialpressure ratio (P(H₂O)/P(H₂) between H₂O and H₂ in the reductionatmosphere, the average heating rate in a temperature range of 600° C.to 750° C., and the maximum heating temperature) shown in Tables 11 to14 and thus base steel sheets were obtained.

The base steel sheets were subjected to a cooling treatment under theconditions (cooling rate 1 (the average cooling rate in a temperaturerange of 760° C. to 700° C.), cooling rate 2 (the average cooling ratein a temperature range of 650° C. to 500° C.), the conditions formartensitic transformation treatment (the treatment temperature and thetreatment time), and bainitic transformation treatment 1 (the treatmenttemperature and the treatment time)) for the cooling step before platingshown in Tables 15 to 18 and thus base steel sheets for platingtreatment were obtained.

Next, the steel sheets were immersed in a zinc plating bath under theconditions (the amount of effective Al, the plating bath temperature,and the steel sheet entering temperature) shown in Tables 15 to 18, anda cooling treatment after plating was performed under the conditions(Expression (2), cooling rate 3 (the average cooling rate in atemperature range of 350° C. to 250° C.), the conditions (the treatmenttemperature and the treatment time) for bainitic transformationtreatment 2, and the conditions (the treatment temperature and thetreatment time) for the reheating treatment) shown in Tables 19 to 22.Next, a bending-bending back deformation was performed under theconditions (the roll diameters and the processing times) shown in Tables19 to 22.

Further, cold rolling was performed under the conditions (rollingreduction) shown in Tables 19 to 22 to obtain hot-dip galvanized steelsheets of Experimental Examples 1 to 200 (wherein the experiment wasstopped in some of experimental examples).

Next, a thickness cross section parallel to the rolling direction of thebase steel sheet was set as an observed section and a sample wascollected from each of the hot-dip galvanized plated steel sheets, andthe microstructure observation with a field emission scanning electronmicroscope (FE-SEM) and high resolution crystal orientation analysisaccording to an EBSD method were performed on the observed section ofthe sample. Volume fractions of the microstructure in a range of ⅛thickness to ⅜ thickness centered at the position of ¼ of the thicknessfrom the surface of the base steel sheet (¼ thickness), and a surfacelayer range originating from an interface between a plated layer and abase steel sheet and having 20 μm depth (surface layer of base steel)were measured respectively.

Here, “martensite” in the tables indicates a fresh martensite, “others”among the microstructures in the tables indicates pearlite and/or coarsecementite. In addition, “hard phase” is a hard structure consisting ofone or more of a bainite, a bainitic ferrite, a fresh martensite and atempered martensite.

Further, a thickness cross section parallel to the rolling direction ofthe steel sheet was set as an observed section and a sample wascollected from the hot-dip galvanized steel sheet. The observed sectionof the sample was observed with a field emission scanning electronmicroscope (FE-SEM) to observe the interface between the plated layerand the base steel sheet, and the ratio of the interface between the ζphase and the base steel sheet in the interface between the plated layerand the base steel sheet (boundary surface occupancy ratio) is measured.“Occupancy ratio of ζ grain in which oxides present” indicates the ratioof the interface between the ζ grains in which coarse oxides are presentamong the ζ grains and the base steel with respect to the entireinterface between the ζ phase and the base steel.

The hot-dip galvanized steel sheet is processed by ion milling and a BSEimage was photographed at an accelerating voltage of 5 kV and amagnification of 5,000 with FE-SEM. Oxides and ζ phase boundaries appeardarker in this BSE image. Among a plated layer/base steel sheet boundarylength, a length in which the ζ phase is formed and a length in whichthe ζ phase including coarse grains is formed are read from the imageand the occupancy ratio of the grains in which oxides present.

FIG. 2 indicates an enlarged cross section structure micrograph of thehot-dip galvanized steel sheet of Experimental Example No. 1. The resultof polishing a cross section of an obtained hot-dip galvanized steelsheet sample by ion milling process and imaging a BSE image at anaccelerating voltage of 5 kV is indicated in FIG. 2. As shown in FIG. 2,a refined layer in which grains are fine was formed in the surface layerof the base steel sheet was formed. Additionally, it was confirmed thatSi—Mn inside oxides are formed at an interface at a plated-layer side ofthe refined layer.

The plated amount of the plating was obtained by melting the platedlayer using a hydrochloric acid with an inhibitor and comparing theweight before and after the melting. The results of observation of themicrostructures and compositions of the plated layers, and so on, of thesamples explained above are indicated in Tables 23 to 34.

Next, in order to investigate the properties of each hot-dip galvanizedsteel sheet, a tensile test, a hole expansion test, a bending test, afatigue test, an adhesion evaluation test, a spot welding test, and acorrosion test were performed. The properties in each experimentalexample are shown in Tables 35 to 42.

No. 5 test pieces as described in JIS Z 2201 were cut out from thehot-dip galvanized steel sheets to perform a tensile test according tothe method described in JIS Z 2241. Thus, the yield strength YS, themaximum tensile strength TS, and the total elongation El were obtained.The strength were evaluated such that a case in which the maximumtensile strength TS was 550 MPa or more was satisfactory.

A hole expansion test was performed according to the method described inJIS Z 2256. Among the formabilities, the ductility El and holeexpansibility λ change according to the maximum tensile strength TS.However, the strength, the ductility and the hole expansibility in thecase in which the following Expression (4) was satisfied weresatisfactory.TS^(1.5)×El×λ^(0.5)≥2.5×10⁶  Expression (4)

No. 5 test pieces as described in JIS Z 2201 were cut out from thehot-dip galvanized steel sheets to perform a bending test which is a 90°V bending test according to the V block method described in JIS Z 2248.A radius at a bottom portion of a V block is varied from 1.0 mm to 6.0mm at intervals of 0.5 mm, a smallest radius of which crack did notoccur in a test piece is set as a minimum bending radius r [mm].Bendability was evaluated by “r/t” obtained by normalizing the minimumbending radius r with the plate thickness t [mm], and a case where “r/t”was 2.0 or less was evaluated as good bendability.

No. 1 test pieces as described in JIS Z 2275 were cut out from thehot-dip galvanized steel sheets to perform a pulsating plane bendingfatigue test according to the method described in JIS Z 2273. Fatiguelimit DL and fatigue limit ratio DL/TS were evaluated by setting themaximum number of repetitions to 10 million times, and a case where thefatigue limit ratio was 0.30 or more was evaluated as good fatigueresistance.

For plating adhesion, each hot-dip galvanized steel sheet to which 5%uniaxial tension strain was applied was subjected to a DuPont impacttest. An adhesive tape was attached to the plated steel sheet after theimpact test and then peeled off. The case in which the plating was notpeeled off was evaluated as pass (o) and the case in which the platingwas peeled off was evaluated as fail (x). The DuPont impact test wasperformed by dropping a weight of 3 kg onto the steel sheet from aheight of 1 m using a punching die having a radius of curvature of thefront end of ½ inches.

Spot weldability was evaluated by performing a continuous dotting test.Under the condition that the diameter of the welded part is 5.3 to 5.7times the square root of the thickness, spot welding was continuouslyperformed 1,000 times and d₁ of the first dot and d₁₀₀₀ of the 1,000-thdot of the diameters of the welded parts were compared to each other.The case in which d₁₀₀₀/d₁ was 0.90 or more was evaluated as pass (∘)and the case in which d₁₀₀₀/d₁ was less than 0.90 was evaluated as fail(x).

For the evaluation of corrosion resistance, a test piece cut out fromeach hot-dip galvanized steel sheet to have a size of 150×70 mm wasused, and the test piece was subjected to a zinc phosphate-based dippingtype chemical conversion treatment and subsequently a cation electrodeposition coat of 20 μm was applied. Further, an intermediate coat of 35μm and an upper coat of 35 μm were applied and then the rear surface andthe end portion were sealed with an insulating tape. In the corrosionresistance test, CCT having one cycle of SST 6 hr→drying 4 hr→wetting 4hr→freezing 4 hr was used. The evaluation of corrosion resistance aftercoating was performed such that the coated surface was cross-cut with acutter until the cutting reached the base steel and a swollen widthafter 60 cycles of CCT was measured. The case in which the swollen widthwas 3.0 mm or less was evaluated as pass (∘) and the case in which theswollen width was more than 3.0 mm was evaluated as fail (x).

For evaluating chipping properties, a test sample was cut out from eachhot-dip galvanized steel sheet to have a size of 70 mm×150 mm, and anautomotive degreasing, chemical conversion and 3-coat coating wereperformed on the test sample. In a state in which the test sample wascooled and retained at −20° C., ten crushed stones (0.3 to 0.5 g) werevertically applied with an air pressure of 2 kgf/cm². Ten crushed stoneswere applied to each sample. Each standard N5 is performed, 50 chippingscars in total were observed and evaluated according to the position ofthe peeled interface. The case in which the peeled interface was abovethe plated layer (the interface between the plated layer and thechemical conversion coating film or the interface between the electrodeposition coat and the intermediate coat coating) was evaluated as (∘)and the case in which even one interface peeling occurred at interfacebetween the plated layer and the base steel (base steel sheet) wasevaluated as (x).

Powdering properties were evaluated using V bending (JIS Z 2248) toevaluate the workability of the plated layer. Each hot-dip galvanizedsteel sheet was cut into a size of 50×90 mm and a formed body was usedwith a 1R-90° V-shaped die press. In the grooves, tape peeling wasperformed. A cellophane tape having a width of 24 mm was pressed on thebent part and then peeled off. The part of the cellophane tape at alength of 90 mm was visually determined. The evaluation criteria were asfollows.

∘: the peeling of the plated layer occurred in an area of less than 5%of the worked part area

x: the peeling of the plated layer occurred in an area of more than 5%of the worked part area

TABLE 1 Chemical C Si Mn P S Al N O components % by mass % by mass % bymass % by mass % by mass % by mass % by mass % by mass A 0.085 0.86 1.920.005 0.0016 0.059 0.0035 0.0008 Example B 0.051 0.51 2.38 0.012 0.00150.035 0.0014 0.0011 Example C 0.097 1.47 3.00 0.005 0.0011 0.007 0.00080.0032 Example D 0.060 1.09 1.35 0.009 0.0005 0.020 0.0047 0.0017Example E 0.180 1.15 1.28 0.005 0.0030 0.042 0.0020 0.0012 Example F0.107 0.60 2.95 0.015 0.0034 0.035 0.0013 0.0010 Example G 0.208 0.382.35 0.008 0.0048 0.028 0.0014 0.0010 Example H 0.078 1.19 3.09 0.0120.0038 0.086 0.0008 0.0020 Example I 0.115 0.22 2.94 0.008 0.0040 1.2460.0022 0.0019 Example J 0.234 0.94 1.44 0.017 0.0003 0.038 0.0017 0.0025Example K 0.268 0.76 2.87 0.016 0.0040 0.081 0.0050 0.0018 Example L0.153 0.94 2.41 0.011 0.0015 0.004 0.0030 0.0027 Example M 0.091 0.371.56 0.014 0.0008 0.046 0.0026 0.0008 Example N 0.203 0.33 2.49 0.0120.0029 0.016 0.0008 0.0012 Example O 0.075 1.90 2.00 0.010 0.0029 0.0270.0041 0.0015 Example P 0.063 0.66 2.31 0.015 0.0027 0.099 0.0027 0.0004Example Q 0.116 0.72 1.96 0.017 0.0029 0.018 0.0046 0.0020 Example R0.081 0.50 2.39 0.009 0.0062 0.072 0.0036 0.0023 Example S 0.203 0.891.74 0.016 0.0016 0.061 0.0008 0.0021 Example T 0.157 0.50 3.16 0.0110.0025 0.041 0.0046 0.0009 Example U 0.100 0.88 2.73 0.047 0.0032 0.0280.0033 0.0015 Example V 0.083 0.65 1.30 0.014 0.0009 0.066 0.0013 0.0012Example W 0.092 0.67 2.86 0.018 0.0012 0.036 0.0020 0.0012 Example X0.069 0.60 2.03 0.007 0.0004 0.043 0.0018 0.0032 Example Y 0.097 1.002.31 0.011 0.0059 0.029 0.0037 0.0020 Example Z 0.106 0.53 2.28 0.0060.0031 0.008 0.0043 0.0022 Example

TABLE 2 Ti Nb V Cr Ni Cu Mo B W Ca Ce Mg Zr La REM Chemical % % % % % %% % % % % % % % % com- by by by by by by by by by by by by by by byponents mass mass mass mass mass mass mass mass mass mass mass mass massmass mass A Example B Example C Example D Example E Example F Example GExample H 0.058 Example I Example J Example K Example L Example M 0.049Example N 0.49 Example O Example P 0.131 Example Q 0.26 Example RExample S 0.41 Example T Example U Example V 0.48 Example W 0.18 ExampleX 0.0047 Example Y 0.0045 Example Z 0.0032 Example

TABLE 3 Chemical C Si Mn P S Al N O components % by mass % by mass % bymass % by mass % by mass % by mass % by mass % by mass AA 0.204 1.032.49 0.012 0.0014 0.047 0.0045 0.0003 Example AB 0.176 0.16 2.06 0.0230.0016 0.083 0.0017 0.0013 Example AC 0.086 1.08 1.60 0.018 0.0006 0.0780.0018 0.0008 Example AD 0.141 0.66 2.28 0.004 0.0009 0.038 0.00590.0016 Example AE 0.138 0.46 2.95 0.016 0.0016 0.020 0.0040 0.0017Example AF 0.124 0.93 1.92 0.017 0.0027 0.057 0.0008 0.0007 Example AG0.158 0.86 2.90 0.009 0.0003 0.070 0.0030 0.0028 Example AH 0.172 0.762.99 0.018 0.0031 0.059 0.0050 0.0013 Example AI 0.075 0.65 2.04 0.0130.0004 0.255 0.0009 0.0010 Example AJ 0.157 0.49 2.07 0.010 0.0013 0.4720.0020 0.0009 Example AK 0.179 0.95 3.07 0.020 0.0043 0.009 0.00160.0008 Example AL 0.096 0.16 2.25 0.006 0.0025 0.008 0.0051 0.0015Example AM 0.177 0.75 2.40 0.009 0.0004 0.756 0.0038 0.0014 Example AN0.150 0.49 1.83 0.010 0.0031 0.068 0.0040 0.0008 Example AO 0.134 0.672.36 0.009 0.0038 0.041 0.0017 0.0025 Example AP 0.170 0.34 2.34 0.0100.0020 0.025 0.0024 0.0008 Example AQ 0.124 0.37 1.22 0.017 0.0064 0.0460.0023 0.0027 Example AR 0.084 0.53 2.20 0.011 0.0053 0.058 0.00130.0017 Example AS 0.135 0.90 2.37 0.017 0.0023 0.061 0.0036 0.0025Example AT 0.084 0.61 2.63 0.004 0.0049 0.033 0.0021 0.0014 Example AU0.086 0.50 2.29 0.004 0.0022 0.045 0.0032 0.0014 Example AV 0.114 0.991.79 0.005 0.0032 0.084 0.0038 0.0014 Example AW 0.157 0.50 2.20 0.0170.0022 0.087 0.0011 0.0009 Example AX 0.090 0.55 3.20 0.003 0.0017 0.0510.0033 0.0007 Example AY 0.186 1.10 1.97 0.010 0.0033 0.030 0.00600.0029 Example AZ 0.070 0.75 2.36 0.015 0.0045 0.040 0.0083 0.0009Example

TABLE 4 Ti Nb V Cr Ni Cu Mo B W Ca Ce Mg Zr La REM % % % % % % % % % % %% % % % Chemical by by by by by by by by by by by by by by by componentsmass mass mass mass mass mass mass mass mass mass mass mass mass massmass AA 0.016 0.016 Example AB 0.0046 Example AC 0.0046 Example AD 0.0130.0009 Example AE 0.0006 Example AF 0.0024 Example AG 0.035 0.007 0.150.0003 Example AH 0.007 0.015 0.14 Example AI 0.090 0.025 1.34 ExampleAJ 0.018 0.026 0.36 0.0018 Example AK 0.045 0.011 0.08 0.0030 Example ALExample AM 0.064 0.014 0.95 0.0014 Example AN 0.0025 0.0013 Example AO0.0041 0.0020 Example AP Example AQ 0.0015 0.0021 0.0008 Example ARExample AS 0.006 0.26 Example AT 0.057 0.06 Example AU 0.082 Example AV0.116 Example AW Example AX 0.09 Example AY 0.26 Example AZ Example

TABLE 5 Chemical C Si Mn P S Al N O components % by mass % by mass % bymass % by mass % by mass % by mass % by mass % by mass BA 0.142 0.932.10 0.013 0.0015 0.064 0.0007 0.0053 Example BB 0.136 0.89 3.30 0.0080.0031 0.070 0.0039 0.0006 Example BC 0.096 0.28 2.29 0.009 0.0018 0.0070.0048 0.0022 Example BD 0.149 0.07 1.82 0.012 0.0016 0.037 0.00150.0025 Example BE 0.085 0.91 1.52 0.018 0.0033 0.052 0.0046 0.0022Example BF 0.186 1.06 1.96 0.012 0.0008 0.047 0.0024 0.0022 Example BG0.094 1.33 1.14 0.009 0.0010 0.021 0.0007 0.0028 Example BH 0.157 0.842.84 0.016 0.0044 0.211 0.0018 0.0012 Example BI 0.109 1.49 0.71 0.0140.0024 0.068 0.0060 0.0006 Example BJ 0.127 0.67 1.53 0.003 0.0036 0.0110.0017 0.0024 Example BK 0.096 0.44 1.96 0.013 0.0049 0.063 0.00170.0027 Example BL 0.092 0.55 2.90 0.006 0.0044 0.016 0.0017 0.0005Example BM 0.120 1.73 0.91 0.009 0.0024 0.010 0.0036 0.0015 Example BN0.102 0.11 1.81 0.004 0.0005 0.254 0.0030 0.0027 Example BO 0.016 1.112.91 0.013 0.0026 0.041 0.0027 0.0017 Comp. Ex. BP 0.411 0.80 2.60 0.0040.0047 0.039 0.0040 0.0020 Comp. Ex. BQ 0.141 0.01 2.03 0.006 0.00250.016 0.0025 0.0029 Comp. Ex. BR 0.126 2.40 2.92 0.012 0.0014 0.0400.0017 0.0016 Comp. Ex. BS 0.121 0.64 0.17 0.008 0.0037 0.042 0.00420.0034 Comp. Ex. BT 0.158 0.89 4.09 0.009 0.0016 0.083 0.0026 0.0018Comp. Ex. BU 0.086 0.77 2.54 0.208 0.0026 0.034 0.0014 0.0024 Comp. Ex.BV 0.147 0.56 2.07 0.010 0.0139 0.043 0.0023 0.0008 Comp. Ex. BW 0.1370.57 2.16 0.017 0.0034 2.077 0.0033 0.0021 Comp. Ex. BX 0.134 0.53 2.300.013 0.0021 0.026 0.0188 0.0022 Comp. Ex. BY 0.190 0.98 2.94 0.0100.0034 0.050 0.0032 0.0154 Comp. Ex.

TABLE 6 Ti Nb V Cr Ni Cu Mo B W Ca Ce Mg Zr La REM % % % % % % % % % % %% % % % Chemical by by by by by by by by by by by by by by by componentsmass mass mass mass mass mass mass mass mass mass mass mass mass massmass BA Example BB Example BC Example BD Example BE 0.61 0.28 Example BFExample BG Example BH Example BI 0.72 0.11 Example BJ 0.074 Example BK0.015 Example BL 0.0063 Example BM 0.005 0.030 0.0025 Example BN 0.0600.018 0.0032 Example BO Comp. Ex. BP Comp. Ex. BQ Comp. Ex. BR Comp. Ex.BS Comp. Ex. BT Comp. Ex. BU Comp. Ex. BV Comp. Ex. BW Comp. Ex. BXComp. Ex. BY Comp. Ex.

TABLE 7 Cold rolling Hot rolling step step Slab heating Rollingcompletion Average Coiling Rolling Experimental Chemical temperaturetemperature cooling rate temperature Ae3* Expression reduction Examplecomponents ° C. ° C. ° C./sec ° C. ° C. (1) % 1 A 1205 913 22 538 8632.2 63 Example 2 A 1225 914 15 601 863 3.6 57 Comp. Ex. 3 A 1235 939 42642 863 5.3 38 Example 4 A 1190 887 76 508 863 1.2 57 Example 5 B 1195888 22 545 836 1.8 61 Example 6 B 1160 913 37 505 836 1.4 54 Example 7 B1230 933 19 608 836 2.5 45 Example 8 B 1220 903 49 576 836 2.0 69Example 9 C 1205 907 15 592 845 5.0 56 Example 10 C 1180 943 21 647 84517.2  69 Example 11 C 1210 916 16 621 845 11.7  66 Example 12 C 1205 90619 600 845 5.7 35 Comp. Ex. 13 D 1215 940 22 609 882 4.1 44 Example 14 D1185 908 21 487 882 3.3 62 Comp. Ex. 15 D 1225 892 61 465 882 2.1 56Example 16 D 1235 915 15 600 882 4.7 70 Example 17 E 1225 868 22 608 8894.6 58 Example 18 E 1195 903 20 601 889 4.9 25 Example 19 E 1190 885 11617 889 6.3 66 Example 20 E 1215 921 20 577 889 3.5 36 Comp. Ex. 21 F1220 939 34 562 822 1.5 48 Example 22 F 1200 911 45 632 822 2.9 54Example 23 F 1210 974 39 572 822 1.5 65 Example 24 F 1210 934 58 596 8222.0 52 Example 25 G 1250 910 22 568 832 1.7 46 Example 26 G 1210 880 65524 832 0.9 59 Example 27 G 1225 891 54 508 832 0.6 58 Comp. Ex. 28 G1245 896 15 596 832 2.1 67 Example 29 H 1235 915 50 602 843 3.9 52Example 30 H 1265 917 53 552 843 2.2 45 Example 31 H 1255 904 34 564 8432.5 2 Example 32 I 1245 946 50 581 960 4.1 48 Example 33 I 1245 968 14630 960 6.9 55 Example 34 I 1210 950 58 583 960 3.9 58 Example 35 J 1190891 27 595 877 3.5 26 Example 36 J 1225 868 38 594 877 3.1 48 Example 37J 1175 935 17 578 877 3.4 53 Example 38 K 1190 884 20 584 835 2.4 50Example 39 K 1240 917 16 582 835 2.4 38 Example 40 K 1205 858 17 585 8352.3 51 Example 41 L 1205 925 16 584 845 3.1 59 Example 42 L 1245 955 59578 845 2.1 64 Example 43 L 1210 923 34 552 845 2.2 52 Comp. Ex. 44 M1185 882 15 544 857 2.5 50 Example 45 M 1270 896 15 567 857 2.8 44Example 46 M 1245 955 24 584 857 2.4 47 Comp. Ex. 47 N 1235 914 23 549816 1.6 61 Example 48 N 1255 911 31 569 816 2.4 35 Example 49 N 1235 94623 550 816 1.5 38 Comp. Ex. 50 O 1255 941 18 554 890 4.7 52 Example

TABLE 8 Cold rolling Hot rolling step step Slab heating Rollingcompletion Average Coiling Rolling Experimental Chemical temperaturetemperature cooling rate temperature Ae3* Expression reduction Examplecomponents ° C. ° C. ° C./sec ° C. ° C. (1) % 51 O 1245 890 8 628 89021.7  52 Comp. Ex. 52 O 1215 896 47 603 890 8.1 25 Example 53 O 1185 88110 624 890 12.1  59 Example 54 P 1235 928 22 572 851 2.2 50 Example 55 P1240 909 14 616 851 1.9 42 Example 56 P 1215 925 75 552 851 1.4 47Example 57 Q 1200 890 34 556 842 2.0 50 Example 58 Q 1205 908 58 582 8422.2 36 Example 59 Q 1230 898 63 570 842 2.0 49 Comp. Ex. 60 R 1250 87439 612 840 2.1 70 Example 61 R 1185 880 27 563 840 4.9 39 Example 62 R1240 905 18 554 840 3.0 28 Example 63 S 1230 899 50 547 861 1.8 52Example 64 S 1220 945 20 607 861 5.9 63 Example 65 S 1245 889 16 576 8613.6 29 Comp. Ex. 66 T 1245 908 25 605 813 2.0 57 Example 67 T 1190 91853 606 813 1.7 28 Example 68 T 1225 884 45 564 813 1.8 45 Comp. Ex. 69 U1210 887 17 598 836 3.1 58 Example 70 U 1220 932 17 581 836 3.7 37Example 71 U 1220 888 23 548 836 2.0 29 Example 72 V 1195 942 38 553 8823.0 52 Example 73 V 1220 870 46 581 882 1.4 33 Example 74 V 1225 929 32596 882 2.3 43 Example 75 W 1200 943 16 613 827 3.2 53 Example 76 W 1250892 29 538 827 1.7 42 Comp. Ex. 77 W 1220 950 37 553 827 3.4 44 Example78 X 1240 894 23 607 850 2.8 37 Example 79 X 1205 940 24 571 850 3.9 44Example 80 X 1225 922 30 591 850 4.8 56 Comp. Ex. 81 Y 1225 891 21 557853 2.7 46 Example 82 Y 1255 888 15 567 853 2.7 36 Example 83 Y 1185 87314 587 853 3.1 63 Example 84 Z 1205 918 17 579 836 2.2 56 Example 85 Z1200 922 16 582 836 1.6 53 Comp. Ex. 86 Z 1205 911 52 619 836 1.4 50Example 87 AA 1235 938 22 601 850 4.0 63 Example 88 AA 1200 886 18 519850 2.4 30 Example 89 AB 1195 913 19 592 840 1.9 58 Example 90 AB 1235926 32 538 840 1.4 28 Example 91 AB 1180 882 49 496 840 1.2 45 Example92 AC 1240 908 21 563 882 3.5 50 Example 93 AC 1205 883 19 635 882 5.556 Example 94 AD 1230 934 61 556 844 1.3 62 Example 95 AD 1195 906 57551 844 1.5 46 Example 96 AE 1235 896 30 542 816 1.6 26 Example 97 AE1195 909 19 613 816 1.4 53 Example 98 AF 1195 932 21 581 865 3.2 63Example 99 AF 1230 914 19 623 865 2.5 53 Example 100 AG 1185 889 48 569838 1.8 52 Example

TABLE 9 Cold rolling Hot rolling step step Slab heating Rollingcompletion Average Coiling Rolling Experimental Chemical temperaturetemperature cooling rate temperature Ae3* Expression reduction Examplecomponents ° C. ° C. ° C./sec ° C. ° C. (1) % 101 AG 1240 942 28 630 8383.4 47 Example 102 AH 1245 916 19 610 826 3.4 75 Example 103 AH 1220 92629 612 826 2.8 56 Example 104 AI 1210 902 14 601 853 3.0 55 Example 105AI 1205 928 22 592 853 2.7 60 Example 106 AJ 1230 921 32 557 903 3.0 63Example 107 AJ 1245 904 29 613 903 2.6 41 Example 108 AK 1235 913 65 545825 1.3 56 Example 109 AK 1210 912 24 609 825 8.4 59 Example 110 AL 1210903 21 551 825 1.5 42 Example 111 AL 1240 878 44 590 825 3.0 59 Example112 AM 1235 938 16 588 915 6.8 57 Example 113 AM 1175 925 22 568 915 5.221 Example 114 AM 1245 889 27 521 915 3.5 36 Example 115 AM 1200 933 14625 915 20.6  42 Comp. Ex. 116 AN 1240 905 20 596 855 2.4 66 Example 117AN 1250 890 30 642 855 3.1 31 Example 118 AO 1225 916 48 585 842 1.8 60Example 119 AO 1225 912 16 555 842 1.8 40 Example 120 AP 1230 905 26 598830 1.7 59 Example 121 AP 1215 897 29 550 830 1.5 50 Example 122 AP 1245959 38 532 830 1.4 49 Example 123 AQ 1235 873 11 599 867 3.2 63 Example124 AQ 1220 936 19 538 867 2.6 58 Example 125 AR 1190 916 15 593 844 2.550 Example 126 AR 1235 929 73 512 844 1.0 38 Example 127 AS 1210 906 20575 847 2.7 40 Example 128 AS 1245 934 24 534 847 1.6 62 Example 129 AT1235 913 22 575 832 2.0 58 Example 130 AT 1210 927 42 621 832 3.0 52Example 131 AU 1180 919 17 571 839 2.2 46 Example 132 AU 1205 881 44 480839 0.7 35 Comp. Ex. 133 AU 1255 873 21 540 839 1.3 41 Example 134 AU1230 902 18 535 839 2.7 49 Example 135 AV 1235 915 28 600 874 3.5 64Example 136 AV 1195 924 52 535 874 2.1 43 Comp. Ex. 137 AV 1210 926 27630 874 4.2 68 Example 138 AW 1200 878 16 560 847 2.4 69 Example 139 AW1230 886 21 539 847 1.6 61 Comp. Ex. 140 AW 1225 954 17 622 847 3.5 37Example 141 AX 1230 939 27 606 813 2.0 48 Example 142 AX 1205 918 53 497813 1.0 53 Example 143 AY 1215 942 31 562 869 2.7 42 Example 144 AY 1210962 21 538 869 9.1 44 Example 145 AZ 1230 896 27 571 845 2.0 74 Example146 AZ 1245 926 15 608 845 2.8 56 Example 147 BA 1215 869 25 564 861 2.456 Example 148 BA 1180 895 27 583 861 3.0 41 Example 149 BB 1215 908 25594 825 3.1 52 Example 150 BB 1170 914 17 553 825 3.0 56 Comp. Ex.

TABLE 10 Cold rolling Hot rolling step step Slab heating Rollingcompletion Average Coiling Rolling Experimental Chemical temperaturetemperature cooling rate temperature Ae3* Expression reduction Examplecomponents ° C. ° C. ° C./sec ° C. ° C. (1) % 151 BB 1235 907 15 574 8253.0 5 Example 152 BB 1185 911 51 551 825 2.5 61 Example 153 BC 1190 92070 545 828 1.0 73 Example 154 BC 1215 879 63 534 828 0.9 59 Example 155BC 1200 899 55 591 828 1.5 55 Example 156 BC 1250 913 28 572 828 1.4 1Example 157 BC 1235 882 55 538 828 0.6 44 Comp. Ex. 158 BD 1240 906 23553 838 1.9 50 Example 159 BD 1235 938 16 606 838 2.6 43 Example 160 BE1230 894 32 568 845 1.9 58 Example 161 BE 1230 898 16 565 845 2.0 41Example 162 BF 1230 914 34 571 867 2.8 60 Example 163 BF 1190 931 66 577867 1.5 48 Example 164 BF 1210 912 27 598 867 2.9 38 Example 165 BF 1195903 16 573 867 3.6 51 Comp. Ex. 166 BG 1250 904 45 573 896 3.6 74Example 167 BG 1175 927 21 590 896 7.3 25 Example 168 BG 1235 908 19 621896 20.3  59 Comp. Ex. 169 BG 1215 879 28 589 896 3.5 62 Example 170 BH1225 886 19 566 854 2.7 63 Example 171 BH 1195 904 29 563 854 1.7 27Comp. Ex. 172 BH 1215 936 58 602 854 2.1 49 Example 173 BH 1240 882 61574 854 1.7 48 Example 174 BI 1210 939 55 558 908 4.0 38 Example 175 BI1195 898 25 516 908 7.9 69 Example 176 BJ 1245 893 48 595 863 2.1 55Example 177 BJ 1195 881 52 528 863 1.8 46 Comp. Ex. 178 BJ 1225 920 35559 863 3.1 46 Example 179 BK 1220 914 52 618 849 2.0 61 Example 180 BK1235 911 62 581 849 2.6 57 Example 181 BL 1190 905 19 604 820 2.6 68Example 182 BL 1185 912 46 582 820 2.4 46 Example 183 BL 1245 916 18 555820 1.9 39 Comp. Ex. 184 BL 1210 890 56 575 820 1.3 65 Example 185 BM1215 925 28 589 914 5.7 42 Example 186 BM 1250 903 53 601 914 13.9  50Comp. Ex. 187 BM 1215 944 12 637 914 15.4  45 Example 188 BN 1240 890 18605 867 2.5 50 Example 189 BN 1220 946 32 548 867 2.7 57 Example 190 BO1225 939 24 575 840 2.9 56 Comp. Ex. 191 BP 1250 893 57 578 839 1.9 52Comp. Ex. 192 BQ 1220 907 29 574 828 1.4 59 Comp. Ex. 193 BR Experimentstopped due to occurrence of cracking of slab during heating in hotrolling step Comp. Ex. 194 BS 1180 909 16 555 905 5.4 53 Comp. Ex. 195BT Experiment stopped due to occurrence of cracking of slab duringheating in hot rolling step Comp. Ex. 196 BU Experiment stopped due tooccurrence of cracking of slab during heating in hot rolling step Comp.Ex. 197 BV 1225 939 23 561 847 2.1 62 Comp. Ex. 198 BW Experimentstopped due to occurrence of cracking of slab during transportationafter casting of slab Comp. Ex. 199 BX 1245 876 47 583 838 1.7 50 Comp.Ex. 200 BY 1215 916 50 594 836 2.9 40 Comp. Ex. 201 A 1205 913 22 538863 2.2 63 Comp. Ex.

TABLE 11 Annealing step Heating step Maximum heating PreheatingReduction zone Experimental Chemical Average heating rate temperature TmAc3 Ac3 − T_(M) Ac1 T_(M) − Ac1 zone P(H2O)/ Example components ° C./sec° C. ° C. ° C. ° C. ° C. Air ratio P(H2) 1 A 2.5 813 861 48 712 101 1.00.45 Example 2 A 2.6 801 861 60 712 89 1.1 0.71 Comp. Ex. 3 A 1.3 796861 65 712 84 0.8 0.52 Example 4 A 2.0 809 861 52 712 97 0.9 0.63Example 5 B 2.3 805 852 47 693 112 1.1 0.86 Example 6 B 2.4 797 852 55693 104 1.1 0.71 Example 7 B 2.9 829 852 23 693 136 0.9 1.17 Example 8 B2.4 794 852 58 693 101 0.9 0.004 Example 9 C 1.9 805 847 42 703 102 0.90.73 Example 10 C 3.3 789 847 58 703 86 1.0 0.27 Example 11 C 2.5 789847 58 703 86 0.9 0.57 Example 12 C 2.7 791 847 56 703 88 1.0 0.86 Comp.Ex. 13 D 3.3 831 892 61 728 103 1.1 0.76 Example 14 D 4.0 810 892 82 72882 1.4 0.55 Comp. Ex. 15 D 2.0 819 892 73 728 91 1.0 0.87 Example 16 D2.2 817 892 75 728 89 1.0 0.66 Example 17 E 2.0 825 867 42 733 92 1.00.54 Example 18 E 2.3 799 867 68 733 66 1.1 0.92 Example 19 E 2.1 812867 55 733 79 0.9 1.11 Example 20 E 2.8 816 867 51 733 83 1.0 0.81 Comp.Ex. 21 F 2.0 777 824 47 686 91 0.9 0.62 Example 22 F 2.4 768 824 56 68682 1.0 0.63 Example 23 F 1.6 771 824 53 686 85 0.8 0.25 Example 24 F 2.2768 824 56 686 82 1.0 1.65 Example 25 G 1.8 790 818 28 689 101 0.9 0.52Example 26 G 1.5 787 818 31 689 98 1.0 0.89 Example 27 G 1.6 771 818 47689 82 0.9 0.46 Comp. Ex. 28 G 2.8 813 818 5 689 124 0.8 0.81 Example 29H 2.1 797 856 59 696 101 1.0 0.61 Example 30 H 2.6 781 856 75 696 85 0.90.14 Example 31 H 1.6 799 856 57 696 103 0.8 0.72 Example 32 I 3.2 874987 113 724 150 0.9 0.77 Example 33 I 1.5 865 987 122 724 141 1.2 0.16Example 34 I 1.2 768 987 219 724 44 0.8 0.43 Example 35 J 2.3 799 839 40719 80 1.0 0.93 Example 36 J 3.3 787 839 52 719 68 0.7 0.65 Example 37 J1.8 794 839 45 719 75 1.1 0.001 Example 38 K 1.8 790 808 18 690 100 0.80.40 Example 39 K 1.8 768 808 40 690 78 0.7 0.41 Example 40 K 2.6 765808 43 690 75 1.0 0.88 Example 41 L 2.3 815 843 28 704 111 1.0 0.68Example 42 L 2.1 829 843 14 704 125 0.8 0.53 Example 43 L 3.0 794 843 49704 90 1.0 0.67 Comp. Ex. 44 M 2.1 808 864 56 703 105 1.0 0.64 Example45 M 1.7 804 864 60 703 101 1.0 0.63 Example 46 M 1.5 791 864 73 703 880.5 0.73 Comp. Ex. 47 N 2.3 785 811 26 698 87 0.9 0.89 Example 48 N 2.1785 811 26 698 87 0.9 0.87 Example 49 N 2.6 768 811 43 698 70 1.0 0.79Comp. Ex. 50 O 2.4 828 898 70 729 99 1.1 0.52 Example

TABLE 12 Annealing step Heating step Maximum heating PreheatingReduction zone Experimental Chemical Average heating rate temperature TmAc3 Ac3 − T_(M) Ac1 T_(M) − Ac1 zone P(H2O)/ Example components ° C./sec° C. ° C. ° C. ° C. ° C. Air ratio P(H2) 51 O 3.0 830 898 68 729 101 0.90.43 Comp. Ex. 52 O 3.2 812 898 86 729 83 0.9 0.74 Example 53 O 2.9 813898 85 729 84 1.1 0.88 Example 54 P 2.9 802 868 66 701 101 1.0 0.62Example 55 P 3.6 794 868 74 701 93 0.9 0.01 Example 56 P 3.1 801 868 67701 100 0.8 0.69 Example 57 Q 2.3 804 835 31 693 111 0.8 0.73 Example 58Q 3.3 782 835 53 693 89 1.0 0.75 Example 59 Q 2.6 794 835 41 693 101 0.90.93 Comp. Ex. 60 R 1.7 798 843 45 690 108 0.9 0.79 Example 61 R 1.6 790843 53 690 100 1.1 0.61 Example 62 R 3.6 787 843 56 690 97 0.9 0.86Example 63 S 2.1 810 831 21 713 97 0.8 0.99 Example 64 S 2.0 787 831 44713 74 1.1 0.45 Example 65 S 1.9 789 831 42 713 76 1.1 0.73 Comp. Ex. 66T 2.1 769 811 42 677 92 1.0 0.65 Example 67 T 2.0 794 811 17 677 117 1.00.82 Example 68 T 2.5 828 811 −17 677 151 1.0 0.67 Comp. Ex. 69 U 2.7793 837 44 690 103 1.0 0.67 Example 70 U 2.6 775 837 62 690 85 0.9 0.44Example 71 U 2.5 771 837 66 690 81 0.9 0.42 Example 72 V 2.3 817 883 66720 97 1.0 0.55 Example 73 V 3.8 818 883 65 720 98 1.1 0.74 Example 74 V2.8 816 883 67 720 96 1.0 0.71 Example 75 W 3.0 786 836 50 685 101 1.00.79 Example 76 W 2.0 778 836 58 685 93 1.0 3.20 Comp. Ex. 77 W 1.7 781836 55 685 96 1.0 0.83 Example 78 X 1.9 808 860 52 699 109 1.0 0.92Example 79 X 3.0 796 860 64 699 97 1.0 0.91 Example 80 X 2.0 796 860 64699 97 0.9 1.15 Comp. Ex. 81 Y 2.5 818 852 34 704 114 0.9 0.80 Example82 Y 1.8 802 852 50 704 98 0.9 0.90 Example 83 Y 2.4 789 852 63 704 851.0 0.26 Example 84 Z 3.0 803 849 46 698 105 0.9 0.85 Example 85 Z 0.6773 849 76 698 75 0.9 0.75 Comp. Ex. 86 Z 2.9 790 849 59 698 92 0.9 0.78Example 87 AA 2.4 813 841 28 703 110 1.2 0.56 Example 88 AA 2.4 783 84158 703 80 1.0 0.46 Example 89 AB 2.5 793 832 39 695 98 0.9 0.74 Example90 AB 2.2 782 832 50 695 87 1.0 0.74 Example 91 AB 1.6 794 832 38 695 990.9 0.16 Example 92 AC 2.1 834 886 52 720 114 0.9 0.68 Example 93 AC 2.4806 886 80 720 86 0.8 0.83 Example 94 AD 2.7 795 839 44 702 93 0.8 0.73Example 95 AD 2.1 793 839 46 702 91 1.1 0.81 Example 96 AE 1.7 774 82147 675 99 1.0 0.70 Example 97 AE 3.2 782 821 39 675 107 0.8 0.77 Example98 AF 1.9 822 868 46 711 111 0.9 0.89 Example 99 AF 1.9 806 868 62 71195 0.9 0.86 Example 100 AG 3.0 795 828 33 694 101 1.0 0.61 Example

TABLE 13 Annealing step Heating step Maximum heating PreheatingReduction zone Experimental Chemical Average heating rate temperature TmAc3 Ac3 − T_(M) Ac1 T_(M) − Ac1 zone P(H2O)/ Example components ° C./sec° C. ° C. ° C. ° C. ° C. Air ratio P(H2) 101 AG 1.2 786 828 42 694 920.8 0.94 Example 102 AH 2.2 784 822 38 689 95 1.0 0.70 Example 103 AH2.5 777 822 45 689 88 0.8 0.48 Example 104 AI 2.9 802 820 18 745 57 1.10.59 Example 105 AI 2.6 772 820 48 745 27 0.8 0.84 Example 106 AJ 1.6820 872 52 720 100 0.9 0.74 Example 107 AJ 2.2 807 872 65 720 87 0.90.83 Example 108 AK 2.4 773 819 46 686 87 1.0 0.77 Example 109 AK 2.2782 819 37 686 96 0.9 0.80 Example 110 AL 2.1 793 828 35 684 109 0.90.89 Example 111 AL 2.7 776 828 52 684 92 1.0 0.73 Example 112 AM 2.5831 880 49 750 81 1.0 0.71 Example 113 AM 1.9 811 880 69 750 61 0.9 0.57Example 114 AM 2.3 853 880 27 750 103 1.0 0.62 Example 115 AM 2.5 824880 56 750 74 0.8 0.98 Comp. Ex. 116 AN 2.7 796 835 39 708 88 0.8 0.65Example 117 AN 2.8 786 835 49 708 78 0.7 0.47 Example 118 AO 3.6 805 83631 707 98 1.0 0.41 Example 119 AO 1.8 781 836 55 707 74 1.1 0.58 Example120 AP 2.3 790 815 25 691 99 1.0 0.74 Example 121 AP 2.3 772 815 43 69181 0.9 0.44 Example 122 AP 1.9 779 815 36 691 88 0.8 0.79 Example 123 AQ3.6 795 855 60 713 82 1.1 0.93 Example 124 AQ 2.0 796 855 59 713 83 1.10.78 Example 125 AR 2.2 800 846 46 696 104 1.0 0.96 Example 126 AR 2.6785 846 61 696 89 1.1 0.59 Example 127 AS 3.0 815 845 30 707 108 1.10.63 Example 128 AS 3.5 788 845 57 707 81 1.0 0.52 Example 129 AT 2.9785 840 55 687 98 1.0 0.99 Example 130 AT 1.5 777 840 63 687 90 1.0 0.56Example 131 AU 2.2 805 845 40 695 110 0.9 0.62 Example 132 AU 1.7 787845 58 695 92 1.0 0.41 Comp. Ex. 133 AU 2.2 795 845 50 695 100 1.0 0.02Example 134 AU 2.1 793 845 52 695 98 0.9 0.69 Example 135 AV 3.3 827 86336 722 105 0.9 0.76 Example 136 AV 3.0 804 863 59 722 82 1.2 0.50 Comp.Ex. 137 AV 3.4 801 863 62 722 79 1.0 0.51 Example 138 AW 3.0 799 839 40696 103 0.9 0.58 Example 139 AW 2.2 792 839 47 696 96 1.1 0.71 Comp. Ex.140 AW 4.4 777 839 62 696 81 1.0 1.12 Example 141 AX 3.6 785 827 42 682103 1.0 0.63 Example 142 AX 2.1 774 827 53 682 92 0.9 0.86 Example 143AY 2.2 809 845 36 716 93 0.8 0.97 Example 144 AY 2.8 795 845 50 716 791.0 0.62 Example 145 AZ 1.8 793 857 64 699 94 0.8 0.60 Example 146 AZ2.5 796 857 61 699 97 0.9 0.47 Example 147 BA 3.3 803 850 47 708 95 0.90.45 Example 148 BA 2.8 789 850 61 708 81 1.0 1.08 Example 149 BB 2.1785 820 35 682 103 0.9 0.79 Example 150 BB 2.5 782 820 38 682 100 1.00.72 Comp. Ex.

TABLE 14 Annealing step Heating step Maximum heating PreheatingReduction zone Experimental Chemical Average heating rate temperature TmAc3 Ac3 − T_(M) Ac1 T_(M) − Ac1 zone P(H2O)/ Example components ° C./sec° C. ° C. ° C. ° C. ° C. Air ratio P(H2) 151 BB 1.5 775 820 45 682 930.8 0.81 Example 152 BB 1.6 772 820 48 682 90 1.1 0.83 Example 153 BC2.3 787 836 49 688 99 1.0 0.71 Example 154 BC 2.8 796 836 40 688 108 0.9 0.86 Example 155 BC 3.9 785 836 51 688 97 0.9 1.31 Example 156 BC2.8 780 836 56 688 92 0.9 0.83 Example 157 BC 2.5 792 836 44 688 104 1.1 0.77 Comp. Ex. 158 BD 2.3 798 832 34 698 100  0.9 0.64 Example 159BD 1.8 780 832 52 698 82 0.8 0.52 Example 160 BE 3.4 802 855 53 696 106 1.0 0.83 Example 161 BE 2.8 802 855 53 696 106  1.2 0.76 Example 162 BF2.7 797 845 48 712 85 1.0 0.76 Example 163 BF 1.9 785 845 60 712 73 1.00.01 Example 164 BF 2.4 794 845 51 712 82 1.0 0.88 Example 165 BF 2.6805 845 40 712 93 1.1 0.68 Comp. Ex. 166 BG 2.9 839 901 62 736 103  1.10.85 Example 167 BG 2.5 824 901 77 736 88 0.8 0.63 Example 168 BG 2.0816 901 85 736 80 1.1 0.79 Comp. Ex. 169 BG 2.4 813 901 88 736 77 1.20.58 Example 170 BH 2.7 792 837 45 696 96 3.0 0.76 Example 171 BH 3.5782 837 55 696 86 1.0  0.0000 Comp. Ex. 172 BH 2.2 792 837 45 696 96 0.90.43 Example 173 BH 3.2 783 837 54 696 87 1.0 0.47 Example 174 BI 3.0860 936 76 741 119  1.0 0.63 Example 175 BI 2.5 830 936 106 741 89 0.90.83 Example 176 BJ 2.2 816 865 49 715 101  1.0 0.68 Example 177 BJ 3.7810 865 55 715 95 0.0 0.59 Comp. Ex. 178 BJ 2.1 806 865 59 715 91 1.00.60 Example 179 BK 2.5 793 845 52 701 92 1.1 0.84 Example 180 BK 4.1792 845 53 701 91 0.9 0.53 Example 181 BL 3.0 783 833 50 681 102  1.00.47 Example 182 BL 3.0 774 833 59 681 93 0.7 0.52 Example 183 BL 1.4773 833 60 681 92 1.0 0.74 Comp. Ex. 184 BL 1.5 783 833 50 681 102  1.00.01 Example 185 BM 3.2 836 917 81 746 90 0.9 0.72 Example 186 BM 2.4763 917 154 746 17 1.1 0.50 Comp. Ex. 187 BM 2.9 837 917 80 746 91 0.80.93 Example 188 BN 2.2 815 861 46 710 105  1.0 0.85 Example 189 BN 2.2798 861 63 710 88 0.9 0.65 Example 190 BO 2.2 845 884 39 792 53 1.0 0.59Comp. Ex. 191 BP 2.9 777 782 5 690 87 0.9 0.71 Comp. Ex. 192 BQ 2.9 794824 30 686 108  0.9 0.65 Comp. Ex. 193 BR Experiment stopped due tooccurrence of cracking of slab during heating in hot rolling step Comp.Ex. 194 BS 2.4 825 892 67 737 88 1.0 0.54 Comp. Ex. 195 BT Experimentstopped due to occurrence of cracking of slab during heating in hotrolling step Comp. Ex. 196 BU Experiment stopped due to occurrence ofcracking of slab during hot rolling in hot rolling step Comp. Ex. 197 BV1.9 810 835 25 703 107  0.8 0.83 Comp. Ex. 198 BW Experiment stopped dueto occurrence of cracking of slab during transportation after casting ofslab Comp. Ex. 199 BX 2.7 804 831 27 693 111  1.1 0.45 Comp. Ex. 200 BY2.6 800 827 27 694 106  1.1 0.73 Comp. Ex. 201 A 2.0 813 861 48 712 101 1.0 2.25 Comp. Ex.

TABLE 15 Annealing step Plating step Cooling step Plating bathMartensitic transformation Bainitic transformation Amount Chem-treatment treatment 1 of Steel sheet Exper- ical Cooling Cooling MsAverage Treatment Average Treatment effective Bath tem- entering imentalcom- rate 1 rate 2 point temperature time temperature time Al peraturetemperature Example ponents ° C./sec ° C./sec ° C. ° C. sec ° C. sec %by mass ° C. ° C. 1 A 1.3 4.2 364 — — — — 0.084 459 467 Example 2 A 1.65.4 350 — — — — 0.042 460 462 Comp. Ex. 3 A 1.3 37.0 323 — — 460 390.095 460 456 Example 4 A 1.1 5.6 250 — — — — 0.094 461 459 Example 5 B1.5 5.8 375 — — — — 0.087 456 460 Example 6 B 1.2 8.0 330 — — — — 0.105466 475 Example 7 B 1.6 6.8 336 307 13 — — 0.133 469 478 Example 8 B 1.27.1 365 — — 420 98 0.107 459 460 Example 9 C 1.4 8.5 296 — — — — 0.104460 465 Example 10 C 1.3 21.9 296 — — — — 0.098 462 461 Example 11 C 1.28.4 296 — — — — 0.097 459 459 Example 12 C 0.9 6.4 275 — — — — 0.120 455457 Comp. Ex. 13 D 1.1 12.1 380 — — — — 0.104 460 467 Example 14 D 1.224.3 343 — — — — 0.075 465 462 Comp. Ex. 15 D 2.3 14.7 401 376 17 — —0.105 461 457 Example 16 D 1.5 13.9 360 346 12 348 26 0.110 460 464Example 17 E 1.0 7.4 236 — — — — 0.084 459 465 Example 18 E 1.3 4.2 243— — — — 0.114 459 456 Example 19 E 2.2 5.1 290 — — — — 0.091 462 460Example 20 E  0.03 6.0 125 — — — — 0.086 462 468 Comp. Ex. 21 F 1.0 3.3275 — — — — 0.109 462 454 Example 22 F 1.3 4.8 302 — — 416 15 0.119 457461 Example 23 F 1.1 4.8 284 — — — — 0.096 461 463 Example 24 F 0.9 2.8254 — — — — 0.080 465 460 Example 25 G 1.0 4.7 102 — — — — 0.108 458 457Example 26 G 2.1 2.9 275 — — — — 0.108 458 460 Example 27 G 0.8 4.9 155— — — — 0.108 463 463 Comp. Ex. 28 G 0.9 7.5 102 — — — — 0.104 462 459Example 29 H 1.0 7.5 294 — — — — 0.101 460 466 Example 30 H 1.6 8.1 320313 42 — — 0.131 461 456 Example 31 H 0.7 5.8 133 — — — — 0.109 463 460Example 32 I 1.1 9.0 276 — — — — 0.096 460 463 Example 33 I 0.9 2.5 288— — 339 83 0.075 459 460 Example 34 I 1.1 10.0 137 — — — — 0.101 459 450Example 35 J 0.8 5.0 107 — — — — 0.106 460 456 Example 36 J 1.5 7.9 225— — 476 21 0.108 462 468 Example 37 J 0.7 13.3 107 — — — — 0.108 457 451Example 38 K 0.9 5.7 68 — — — — 0.095 458 453 Example 39 K 0.8 1.4 149 —— — — 0.106 458 465 Example 40 K 0.8 3.1 149 — — — — 0.096 461 462Example 41 L 1.3 8.1 174 — — — — 0.095 459 464 Example 42 L 2.4 7.7 311221 14 — — 0.096 463 472 Example 43 L 0.9 5.9 164 — — 525 175  0.103 458464 Comp. Ex. 44 M 1.1 6.3 150 — — — — 0.086 459 454 Example 45 M 2.17.0 377 — — 419 248  0.123 463 460 Example 46 M 0.7 6.5 150 — — — —0.082 460 464 Comp. Ex. 47 N 1.3 2.3 188 — — — — 0.086 459 460 Example48 N 1.5 20.3 245 — — — — 0.110 459 467 Example 49 N 5.4 7.0 302 — — 38563 0.090 461 458 Comp. Ex. 50 O 1.2 5.2 306 — — — — 0.096 461 467Example

TABLE 16 Annealing step Plating step Cooling step Plating bathMartensitic transformation Bainitic transformation Amount Chem-treatment treatment 1 of Steel sheet Exper- ical Cooling Cooling MsAverage Treatment Average Treatment effective Bath tem- entering imentalcom- rate 1 rate 2 point temperature time temperature time Al peraturetemperature Example ponents ° C./sec ° C./sec ° C. ° C. sec ° C. sec %by mass ° C. ° C. 51 O 1.2 7.5 295 — — — — 0.110 458 457 Comp. Ex. 52 O1.1 5.2 328 — — — — 0.106 459 457 Example 53 O 1.0 14.4 301 — — — —0.092 460 456 Example 54 P 1.0 4.5 337 — — — — 0.100 461 455 Example 55P 1.3 4.4 359 — — — — 0.106 461 456 Example 56 P 1.2 5.8 345 — — — —0.140 460 461 Example 57 Q 0.9 7.3 114 — — — — 0.113 461 455 Example 58Q 1.4 10.1 296 — — — — 0.099 459 456 Example 59 Q 1.8 6.7 327 307 18 409128 0.107 458 463 Comp. Ex. 60 R 0.8 4.0 24 — — — — 0.087 459 456Example 61 R 0.7 7.5 131 — — — — 0.096 461 462 Example 62 R 0.8 2.2 −97— — — — 0.076 461 465 Example 63 S 1.0 7.6 112 — — — — 0.090 460 464Example 64 S 0.9 39.0 136 — — — — 0.127 460 462 Example 65 S 0.6 7.2 112— — — — 0.102 459 455 Comp. Ex. 66 T 0.8 1.6 148 — — — — 0.096 458 463Example 67 T 1.1 82.1 176 — — 376 413 0.100 460 450 Example 68 T 2.5 2.6321 — — — — 0.106 460 468 Comp. Ex. 69 U 1.1 8.1 236 — — — — 0.108 460456 Example 70 U 1.4 10.0 311 — — — — 0.089 459 458 Example 71 U 1.3 5.9305 — — — — 0.095 460 458 Example 72 V 1.4 5.4 368 — — — — 0.098 462 454Example 73 V 1.7 22.2 381 — — — — 0.131 456 460 Example 74 V 0.4 5.9 159— — — — 0.113 458 457 Example 75 W 1.2 4.7 296 — — — — 0.102 462 448Example 76 W 0.8 7.7 214 — — — — 0.110 457 453 Comp. Ex. 77 W 0.6 2.8141 — — — — 0.091 456 458 Example 78 X 1.1 11.0 135 — — — — 0.110 455447 Example 79 X 1.5 4.1 345 — — — — 0.098 460 464 Example 80 X 1.2 4.3336 — — — — 0.099 459 456 Comp. Ex. 81 Y 1.1 7.8 159 — — — — 0.099 463469 Example 82 Y 2.2 48.0 350 300 27 — — 0.071 458 451 Example 83 Y 1.05.0 276 — — — — 0.086 462 465 Example 84 Z 1.1 4.9 280 — — — — 0.111 462471 Example 85 Z 1.0 7.8 301 — — — — 0.097 462 471 Comp. Ex. 86 Z 0.97.1 189 — — — — 0.090 459 457 Example 87 AA 1.0 12.1 94 — — — — 0.098458 461 Example 88 AA 1.0 4.8 197 — — — — 0.102 457 464 Example 89 AB1.5 4.0 265 — — — — 0.092 459 458 Example 90 AB 1.2 5.3 248 — — 380  450.161 466 467 Example 91 AB 0.7 2.6 120 — — — — 0.098 457 452 Example 92AC 1.1 3.0 130 — — — — 0.096 459 455 Example 93 AC 0.8 4.7 156 — — — —0.100 461 459 Example 94 AD 1.3 2.7 276 — — — — 0.097 458 449 Example 95AD 1.5 7.4 281 — — — — 0.096 458 457 Example 96 AE 1.0 3.0 220 — — — —0.102 461 460 Example 97 AE 1.6 5.7 286 — — 437  26 0.089 461 457Example 98 AF 1.2 3.3 235 — — — — 0.099 459 461 Example 99 AF 2.8 14.5343 — — — — 0.094 461 455 Example 100 AG 0.9 13.4 194 — — — — 0.104 456464 Example

TABLE 17 Annealing step Plating step Cooling step Plating bathMartensitic transformation Bainitic transformation Amount Chem-treatment treatment 1 of Bath Steel sheet ical Cooling Cooling MsAverage Treatment Average Treatment effective temper- enteringExperimental compo- rate 1 rate 2 point temperature time temperaturetime Al ature temperature Example nents ° C./sec ° C./sec ° C. ° C. sec° C. sec % by mass ° C. ° C. 1 A 1.3 4.2 364 — — — — 0.084 459 467Example 2 A 1.6 5.4 350 — — — — 0.042 460 462 Comp. Ex. 3 A 1.3 37.0 323— — 460 39 0.095 460 456 Example 4 A 1.1 5.6 250 — — — — 0.094 461 459Example 5 B 1.5 5.8 375 — — — — 0.087 456 460 Example 6 B 1.2 8.0 330 —— — — 0.105 466 475 Example 7 B 1.6 6.8 336 307 13 — — 0.133 469 478Example 8 B 1.2 7.1 365 — — 420 98 0.107 459 460 Example 9 C 1.4 8.5 296— — — — 0.104 460 465 Example 10 C 1.3 21.9 296 — — — — 0.098 462 461Example 11 C 1.2 8.4 296 — — — — 0.097 459 459 Example 12 C 0.9 6.4 275— — — — 0.120 455 457 Comp. Ex. 13 D 1.1 12.1 380 — — — — 0.104 460 467Example 14 D 1.2 24.3 343 — — — — 0.075 465 462 Comp. Ex. 15 D 2.3 14.7401 376 17 — — 0.105 461 457 Example 16 D 1.5 13.9 360 346 12 348 260.110 460 464 Example 17 E 1.0 7.4 236 — — — — 0.084 459 465 Example 18E 1.3 4.2 243 — — — — 0.114 459 456 Example 19 E 2.2 5.1 290 — — — —0.091 462 460 Example 20 E 0.03 6.0 125 — — — — 0.086 462 468 Comp. Ex.21 F 1.0 3.3 275 — — — — 0.109 462 454 Example 22 F 1.3 4.8 302 — — 41615 0.119 457 461 Example 23 F 1.1 4.8 284 — — — — 0.096 461 463 Example24 F 0.9 2.8 254 — — — — 0.080 465 460 Example 25 G 1.0 4.7 102 — — — —0.108 458 457 Example 26 G 2.1 2.9 275 — — — — 0.108 458 460 Example 27G 0.8 4.9 155 — — — — 0.108 463 463 Comp. Ex. 28 G 0.9 7.5 102 — — — —0.104 462 459 Example 29 H 1.0 7.5 294 — — — — 0.101 460 466 Example 30H 1.6 8.1 320 313 42 — — 0.131 461 456 Example 31 H 0.7 5.8 133 — — — —0.109 463 460 Example 32 I 1.1 9.0 276 — — — — 0.096 460 463 Example 33I 0.9 2.5 288 — — 339 83 0.075 459 460 Example 34 I 1.1 10.0 137 — — — —0.101 459 450 Example 35 J 0.8 5.0 107 — — — — 0.106 460 456 Example 36J 1.5 7.9 225 — — 476 21 0.108 462 468 Example 37 J 0.7 13.3 107 — — — —0.108 457 451 Example 38 K 0.9 5.7 68 — — — — 0.095 458 453 Example 39 K0.8 1.4 149 — — — — 0.106 458 465 Example 40 K 0.8 3.1 149 — — — — 0.096461 462 Example 41 L 1.3 8.1 174 — — — — 0.095 459 464 Example 42 L 2.47.7 311 221 14 — — 0.096 463 472 Example 43 L 0.9 5.9 164 — — 525 175 0.103 458 464 Comp. Ex. 44 M 1.1 6.3 150 — — — — 0.086 459 454 Example45 M 2.1 7.0 377 — — 419 248  0.123 463 460 Example 46 M 0.7 6.5 150 — —— — 0.082 460 464 Comp. Ex. 47 N 1.3 2.3 188 — — — — 0.086 459 460Example 48 N 1.5 20.3 245 — — — — 0.110 459 467 Example 49 N 5.4 7.0 302— — 385 63 0.090 461 458 Comp. Ex. 50 O 1.2 5.2 306 — — — — 0.096 461467 Example

TABLE 18 Annealing step Plating step Cooling step Plating bathMartensitic transformation Bainitic transformation Amount Chem-treatment treatment 1 of Bath Steel sheet ical Cooling Cooling MsAverage Treatment Average Treatment effective temper- enteringExperimental compo- rate 1 rate 2 point temperature time temperaturetime Al ature temperature Example nents ° C./sec ° C./sec ° C. ° C. sec° C. sec % by mass ° C. ° C. 151 BB 1.0 4.8 229 — — 482 40 0.107 459 462Example 152 BB 0.9 1.3 223 — — — — 0.057 455 453 Example 153 BC 0.9 3.3132 — — — — 0.104 458 458 Example 154 BC 1.5 14.5 323 — — — — 0.100 457463 Example 155 BC 1.4 3.8 319 — — — — 0.073 461 455 Example 156 BC 1.03.3 240 — — 453 36 0.110 458 458 Example 157 BC 1.0 6.5 204 — — — —0.099 458 464 Comp. Ex. 158 BD 1.2 9.2 124 — — — — 0.091 458 463 Example159 BD 0.7 2.6 124 — — — — 0.100 461 467 Example 160 BE 1.3 7.1 290 — —— — 0.090 462 468 Example 161 BE 1.1 3.0 196 — — — — 0.129 459 455Example 162 BF 1.0 3.2 212 — — — — 0.110 457 465 Example 163 BF 1.1 3.7231 — — — — 0.100 459 453 Example 164 BF 1.0 14.4 219 — — 458 81 0.078464 469 Example 165 BF 1.3 9.0 219 — — — — 0.109 458 465 Comp. Ex. 166BG 1.1 18.8 139 — — — — 0.091 460 463 Example 167 BG 3.7 2.2 406 — — — —0.131 462 455 Example 168 BG 1.0 2.6 259 — — — — 0.090 463 470 Comp. Ex.169 BG 1.4 7.4 328 — — — — 0.091 459 464 Example 170 BH 1.1 7.5 220 — —— — 0.094 459 462 Example 171 BH 1.9 8.3 271 — — — — 0.110 462 462 Comp.Ex. 172 BH 1.4 34.0 256 — — 394 71 0.068 464 455 Example 173 BH 1.5 16.2271 — — — — 0.117 457 455 Example 174 BI 1.1 4.9 151 — — — — 0.111 462468 Example 175 BI 1.0 4.9 288 — — 463 24 0.101 460 454 Example 176 BJ1.1 4.9 124 — — — — 0.096 461 466 Example 177 BJ 2.0 9.0 315 — — 461810  0.103 462 460 Comp. Ex. 178 BJ 0.9 23.8 124 — — — — 0.092 462 470Example 179 BK 1.0 9.5 142 — — — — 0.107 461 459 Example 180 BK 1.5 14.2341 — — — — 0.101 456 462 Example 181 BL 0.9 8.8 233 — — — — 0.096 463469 Example 182 BL 1.5 35.0 319 278 24 — — 0.112 460 458 Example 183 BL0.8 3.0 233 — — — — 0.082 466 467 Comp. Ex. 184 BL 1.2 1.7 295 — — 47319 0.110 457 451 Example 185 BM 1.0 7.3 212 — — — — 0.104 459 450Example 186 BM 1.5 12.7 −86 — — — — 0.091 461 453 Comp. Ex. 187 BM 1.210.9 246 — — — — 0.098 459 456 Example 188 BN 0.8 6.6 136 — — — — 0.091457 457 Example 189 BN 1.1 3.0 302 — — — — 0.098 462 459 Example 190 BO1.2 3.1 * — — — — 0.096 463 456 Comp. Ex. 191 BP 1.1 3.6 71 — — — —0.097 458 450 Comp. Ex. 192 BQ 0.9 5.2 240 — — — — 0.099 459 462 Comp.Ex. 193 BR Experiment stopped due to occurrence of cracking of slabduring heating in hot rolling step Comp. Ex. 194 BS 1.1 4.9 168 — — — —0.108 458 458 Comp. Ex. 195 BT Experiment stopped due to occurrence ofcracking of slab during heating in hot rolling step Comp. Ex. 196 BUExperiment stopped due to occurrence of cracking of slab during hotrolling in hot rolling step Comp. Ex. 197 BV 1.4 4.2 229 — — — — 0.110459 457 Comp. Ex. 198 BW Experiment stopped due to occurrence ofcracking of slab during transportation after casting of slab Comp. Ex.199 BX 1.7 7.0 255 — — — — 0.091 466 462 Comp. Ex. 200 BY 1.1 2.7 199 —— — — 0.098 462 463 Comp. Ex. 201 A 1.5 7.2 364 — — — — 0.091 459 461Comp. Ex.

TABLE 19 Cooling step after plating Processing Bainitic Bending -bending transformation back Cold treatment 2 Reheating treatmentprocessing rolling Experi- Cooling Treatment Treatment TreatmentTreatment Roll Processing Rolling mental Chemical rate 3 temperaturetime temperature time Expression diameter times reduction Examplecomponents ° C./sec ° C. sec ° C. sec (2) mm times % 1 A 3.2 — — — —1.17 350 2 0.11 Example 2 A 2.0 — — — — 4.57 350 2 0.13 Comp. Ex. 3 A1.9 — — — — 0.90 350 2 0.40 Example 4 A 1.9 — — 291 18 0.59 500 8 0.27Example 5 B 3.5 — — — — 0.94 350 2 0.12 Example 6 B 3.1 — — — — 0.86 3502 0.05 Example 7 B 2.0 — — — — 0.43 350 2 0.25 Example 8 B 2.0 313 38 —— 0.59 350 2 0.81 Example 9 C 3.5 — — — — 0.66 350 2 0.06 Example 10 C3.2 320 61 330  6 0.50 350 2 0.08 Example 11 C 2.4 — — — — 0.70 350 20.15 Example 12 C 2.1 — — — — 0.21 350 2 0.18 Comp. Ex. 13 D 3.5 — — — —0.75 350 2 0.20 Example 14 D 3.3 — — — — 1.53 350 2 0.15 Comp. Ex. 15 D2.3 — — — — 0.70 350 2 0.20 Example 16 D 3.2 — — — — 0.71 700 6 0.09Example 17 E 4.1 — — — — 0.72 350 2 0.19 Example 18 E 2.5 — — 324 380.93 350 2 0.20 Example 19 E 1.7 — — — — 1.24 350 2 0.55 Example 20 E4.2 — — — — 0.82 350 2 0.11 Comp. Ex. 21 F 2.8 — — — — 0.72 350 2 0.49Example 22 F 3.1 — — 310 14 0.53 350 2 0.14 Example 23 F 2.0 336 180  —— 0.62 700 6 0.14 Example 24 F 2.2 — — — — 1.63 350 2 0.18 Example 25 G3.9 — — — — 0.66 350 2 0.16 Example 26 G 2.6 — — 253  6 0.73 700 6 0.10Example 27 G 2.4 — — — — 0.86 350 2 0.18 Comp. Ex. 28 G 2.1 — — — — 0.61350 2 0.05 Example 29 H 2.9 — — — — 0.94 350 2 0.38 Example 30 H 4.3 — —— — 0.43 350 2 0.10 Example 31 H 1.9 — — — — 0.83 350 2 0.19 Example 32I 2.9 — — — — 0.81 350 2 0.22 Example 33 I 2.3 — — 273 16 1.27 350 20.21 Example 34 I 3.8 — — — — 0.73 350 2 1.13 Example 35 J 2.4 — — — —0.77 350 2 0.28 Example 36 J 2.8 — — — — 0.66 700 6 0.24 Example 37 J1.7 — — — — 0.87 350 2 0.19 Example 38 K 2.9 — — — — 0.70 350 2 0.12Example 39 K 1.8 — — — — 0.77 350 2 0.17 Example 40 K 2.1 262 35 — —0.76 350 2 0.15 Example 41 L 3.1 — — — — 0.77 350 2 0.15 Example 42 L2.3 — — — — 0.89 350 2 0.14 Example 43 L 2.3 — — — — 0.84 350 2 0.17Comp. Ex. 44 M 3.7 — — — — 0.74 400 2 0.22 Example 45 M 2.1 — — — — 0.55400 2 0.16 Example 46 M 2.0 — — — — 1.55 400 2 0.13 Comp. Ex. 47 N 4.3 —— — — 1.28 400 2 0.25 Example 48 N 2.2 — — 314 30 0.74 400 2 0.40Example 49 N 3.4 — — — — 0.84 400 2 0.10 Comp. Ex. 50 O 3.1 — — — — 1.11350 2 0.20 Example

TABLE 20 Cooling step after plating Processing Bainitic Bending -bending transformation back Cold treatment 2 Reheating treatmentprocessing rolling Experi- Cooling Treatment Treatment TreatmentTreatment Roll Processing Rolling mental Chemical rate 3 temperaturetime temperature time Expression diameter times reduction Examplecomponents ° C./sec ° C. sec ° C. sec (2) mm times % 51 O 3.2 — — — —0.76 350 2 0.22 Comp. Ex. 52 O 2.8 — — — — 0.46 350 2 0.15 Example 53 O2.5 — — 291 19 0.54 350 2 0.16 Example 54 P 3.2 — — — — 0.73 350 4 0.13Example 55 P 3.2 276 53 — — 0.60 350 4 0.22 Example 56 P 3.1 — — — —0.43 350 4 0.18 Example 57 Q 3.0 — — — — 0.50 350 2 0.23 Example 58 Q3.4 — — — — 0.56 350 2 0.35 Example 59 Q 3.9 268 52 272 22 0.53 1800  20.10 Comp. Ex. 60 R 2.6 — — — — 1.29 350 2 0.05 Example 61 R 1.8 — — — —0.87 350 2 0.09 Example 62 R 3.6 — — 324  9 0.92 350 2 0.10 Example 63 S4.6 — — — — 0.81 400 4 0.48 Example 64 S 2.1 — — — — 0.47 400 4 0.18Example 65 S 2.0 — — — — 0.95 400 4 0.22 Comp. Ex. 66 T 2.8 — — — — 0.83350 2 0.14 Example 67 T 3.0 — — — — 0.64 350 2 0.16 Example 68 T 2.5 — —— — 0.51 350 2 0.09 Comp. Ex. 69 U 4.2 — — — — 0.68 150 2 0.23 Example70 U 3.2 — — — — 0.72 150 2 0.20 Example 71 U 0.4 — — — — 0.70 150 20.19 Example 72 V 2.9 — — — — 0.71 170 2 0.29 Example 73 V 0.5 — — — —0.60 170 2 0.20 Example 74 V 2.7 — — 272 12 0.53 170 2 0.08 Example 75 W3.1 — — — — 0.62 350 2 0.21 Example 76 W 1.5 — — — — 1.13 350 2 0.22Comp. Ex. 77 W 1.4 — — 303 30 0.85 350 2 0.10 Example 78 X 3.8 — — — —0.44 350 2 0.20 Example 79 X 2.8 — — — — 0.68 350 2 0.24 Example 80 X2.4 — — 283 18 0.83  25 2 0.04 Comp. Ex. 81 Y 3.7 — — — — 0.86 350 20.14 Example 82 Y 2.5 — — — — 1.18 350 2 0.17 Example 83 Y 2.3 — — — —1.27 350 2 0.16 Example 84 Z 4.4 — — — — 0.66 350 2 0.08 Example 85 Z2.4 — — — — 0.99 350 2 0.10 Comp. Ex. 86 Z 2.9 — — — — 0.76 350 2 0.08Example 87 AA 3.5 — — — — 0.81 350 2 0.05 Example 88 AA 3.0 — — 325  80.64 350 2 — Example 89 AB 4.5 — — — — 0.64 350 4 0.15 Example 90 AB 2.9— — — — 0.41 350 4 0.21 Example 91 AB 1.2 274 54 — — 0.71 350 4 0.15Example 92 AC 4.7 — — — — 0.71 350 4 0.06 Example 93 AC 2.7 — — — — 0.75350 4 0.26 Example 94 AD 4.7 — — — — 0.83 350 4 0.22 Example 95 AD 2.4 —— 290 30 0.80 350 4 0.29 Example 96 AE 3.4 — — — — 0.82 350 4 0.08Example 97 AE 3.3 — — 284  9 1.00 350 4 0.17 Example 98 AF 3.8 — — — —0.69 350 4 0.22 Example 99 AF 2.7 — — — — 1.08 350 4 0.17 Example 100 AG3.6 — — — — 0.56 350 4 0.19 Example

TABLE 21 Processing Cooling step after plating Bending - bendingBainitic transformation back Cold treatment 2 Reheating treatmentprocessing rolling Experi- Cooling Treatment Treatment TreatmentTreatment Roll Processing Rolling mental Chemical rate 3 temperaturetime temperature time Expression diameter times reduction Examplecomponents ° C./sec ° C. sec ° C. sec (2) mm times % 101 AG 2.6 — — — —1.09 350 4 0.15 Example 102 AH 4.3 — — — — 1.07 600 4 0.10 Example 103AH 2.8 — — — — 0.88 600 4 0.28 Example 104 AI 3.1 — — — — 0.90 350 20.15 Example 105 AI 2.1 — — — — 0.65 350 2 — Example 106 AJ 2.8 — — — —0.83 350 2 0.24 Example 107 AJ 2.6 — — — — 1.39 350 2 0.29 Example 108AK 4.8 — — — — 0.76 350 2 0.19 Example 109 AK 3.8 — — — — 1.17 350 20.19 Example 110 AL 3.4 — — — — 1.10 350 2 0.05 Example 111 AL 3.1 28317 — — 0.86 350 2 0.14 Example 112 AM 3.8 — — — — 0.82 350 2 0.10Example 113 AM 4.5 — — 310 8 1.04 350 2 0.14 Example 114 AM 3.3 270 28 —— 0.76 350 2 0.35 Example 115 AM 2.4 — — — — 0.72 350 2 0.13 Comp. Ex.116 AN 3.2 — — — — 0.85 350 2 0.15 Example 117 AN 2.8 — — — — 0.80 350 20.21 Example 118 AO 3.7 — — — — 0.95 350 2 0.64 Example 119 AO 2.5 — — —— 0.77 350 2 0.10 Example 120 AP 2.7 — — — — 0.72 600 2 0.06 Example 121AP 2.0 — — — — 0.94 600 2 0.38 Example 122 AP 0.6 — — — — 0.89 600 20.09 Example 123 AQ 2.8 — — — — 0.62 600 2 0.13 Example 124 AQ 1.8 — — —— 0.56 600 2 0.75 Example 125 AR 2.2 — — — — 0.84 600 2 0.18 Example 126AR 2.8 — — — — 0.67 600 2 0.13 Example 127 AS 3.7 — — — — 1.04 750 100.08 Example 128 AS 2.6 — — — — 0.48 750 10 0.21 Example 129 AT 5.3 — —— — 0.55 600 2 0.19 Example 130 AT 1.5 — — 285 7 1.35 600 2 0.12 Example131 AU 4.8 — — — — 0.55 350 2 0.13 Example 132 AU 1.9 — — — — 1.06 350 20.23 Comp. Ex. 133 AU 2.5 264 38 — — 0.66 350 2 0.26 Example 134 AU 1.8— — — — 0.59 350 2 0.15 Example 135 AV 4.3 — — — — 0.65 350 2 0.21Example 136 AV 3.5 — — — — 0.92 350 2 0.08 Comp. Ex. 137 AV 4.3 341 24 —— 0.75 350 2 0.09 Example 138 AW 3.2 — — — — 0.74 500 2 0.06 Example 139AW 4.0 — — — — 0.61 500 2 0.40 Comp. Ex. 140 AW 2.8 279 32 — — 0.60 5002 0.07 Example 141 AX 3.8 — — — — 0.64 500 2 0.29 Example 142 AX 2.2 — —— — 0.85 500 2 0.06 Example 143 AY 4.9 — — — — 0.77 500 4 0.28 Example144 AY 3.9 — — — — 0.62 500 4 0.16 Example 145 AZ 2.6 — — — — 0.53 500 40.27 Example 146 AZ 1.6 — — — — 0.69 500 4 0.10 Example 147 BA 4.0 — — —— 0.61 350 2 0.31 Example 148 BA 3.4 — — — — 0.58 350 2 0.06 Example 149BB 4.0 — — — — 0.61 350 2 0.34 Example 150 BB 3.4 — — — — 0.11 350 20.31 Comp. Ex.

TABLE 22 Processing Cooling step after plating Bending - bendingBainitic transformation back Cold treatment 2 Reheating treatmentprocessing rolling Experi- Cooling Treatment Treatment TreatmentTreatment Roll Processing Rolling mental Chemical rate 3 temperaturetime temperature time Expression diameter times reduction Examplecomponents ° C./sec ° C. sec ° C. sec (2) mm times % 151 BB 2.0 — — — —0.75 350 2 0.07 Example 152 BB 1.4 — — — — 2.11 350 2 0.29 Example 153BC 2.5 — — — — 0.65 350 2 0.13 Example 154 BC 3.0 330 21 — — 0.50 350 20.41 Example 155 BC 2.6 — — — — 1.18 350 2 0.12 Example 156 BC 2.0 31590 — — 0.67 350 2 0.23 Example 157 BC 2.4 — — — — 0.64 350 2 0.04 Comp.Ex. 158 BD 3.9 — — — — 0.88 350 2 0.19 Example 159 BD 1.8 — — — — 1.14350 2 0.05 Example 160 BE 4.9 — — — — 0.75 350 2 0.16 Example 161 BE 2.3— — — — 0.69 350 2 0.09 Example 162 BF 2.7 — — — — 0.47 350 2 0.24Example 163 BF 2.4 — — — — 0.60 350 2 0.05 Example 164 BF 2.3 — — — —2.06 350 2 0.10 Example 165 BF 3.8 420 91 — — 0.53 350 2 0.14 Comp. Ex.166 BG 4.2 — — — — 0.89 350 2 0.37 Example 167 BG 2.6 — — 277 19 0.53350 2 0.19 Example 168 BG 2.1 — — — — 1.00 350 2 0.07 Comp. Ex. 169 BG3.6 — — — — 0.46 70 2 0.07 Example 170 BH 3.4 — — — — 0.87 350 2 0.12Example 171 BH 4.1 — — — — 0.55 350 2 0.07 Comp. Ex. 172 BH 2.7 279 19 —— 1.84 350 2 0.23 Example 173 BH 4.1 315 45 — — 0.57 140 2 0.07 Example174 BI 2.5 — — — — 0.58 350 2 0.14 Example 175 BI 2.4 314 20 290 21 0.82350 2 0.15 Example 176 BJ 4.5 — — — — 0.76 350 2 0.22 Example 177 BJ 3.6— — — — 0.54 350 2 0.17 Comp. Ex. 178 BJ 3.2 — — — — 0.62 350 2 0.15Example 179 BK 2.4 — — — — 0.67 350 2 0.17 Example 180 BK 3.5 — — — —0.49 350 2 0.25 Example 181 BL 3.8 — — — — 0.71 350 2 0.50 Example 182BL 2.7 — — — — 0.85 350 2 0.15 Example 183 BL 1.5 — — — — 2.57 350 20.06 Comp. Ex. 184 BL 2.3 — — — — 0.74 350 8 0.07 Example 185 BM 3.3 — —— — 0.74 350 2 0.19 Example 186 BM 2.8 — — — — 0.79 350 2 0.24 Comp. Ex.187 BM 2.8 267 35 — — 0.75 350 2 0.18 Example 188 BN 3.1 — — — — 0.85350 2 0.04 Example 189 BN 2.1 — — 304 14 0.73 350 2 0.06 Example 190 BO3.4 — — — — 0.68 350 2 0.09 Comp. Ex. 191 BP 2.6 — — — — 0.76 350 2 0.28Comp. Ex. 192 BQ 4.8 — — — — 0.71 350 2 0.09 Comp. Ex. 193 BR Experimentstopped due to occurrence of cracking of slab during heating in hotrolling step Comp. Ex. 194 BS 3.3 — — — — 0.53 350 2 0.10 Comp. Ex. 195BT Experiment stopped due to occurrence of cracking of slab duringheating in hot rolling step Comp. Ex. 196 BU Experiment stopped due tooccurrence of cracking of slab during hot rolling in hot rolling stepComp. Ex. 197 BV 3.5 — — — — 0.61 350 2 0.04 Comp. Ex. 198 BW Experimentstopped due to occurrence of cracking of slab during transportationafter casting of slab Comp. Ex. 199 BX 3.5 — — — — 0.93 350 2 0.13 Comp.Ex. 200 BY 3.7 — — — — 0.92 350 2 0.05 Comp. Ex. 201 A 5.0 — — — — 1.07350 2 0.10 Comp. Ex.

TABLE 23 Microstructure Base steel surface layer Grain ¼ thicknessbound- Structure fraction Structure fraction aries Hard Hard and/orExperi- Chemical Bainitic Mar- Tempered Residual phase Residual phaseoxides mental com- Ferrite Bainite ferrite tensite martensite austeniteothers V2 austenite V1 V1/ in Example ponents % % % % % % % % % % V2grains 1 A 59 9 12 17 0 3 0 38 0 28 0.73 none Example 2 A 64 6 8 15 2 23 31 1 17 0.55 none Comp. Ex. 3 A 71 14 13 2 0 0 0 29 0 20 0.70 noneExample 4 A 81 3 3 0 13 0 0 19 0 15 0.77 none Example 5 B 68 11 2 14 3 11 30 0 17 0.56 none Example 6 B 80 6 4 8 0 2 0 18 0 12 0.66 none Example7 B 79 5 2 0 14 0 0 21 0 12 0.59 none Example 8 B 72 14 7 2 0 5 0 23 016 0.68 none Example 9 C 61 0 13 23 0 3 0 36 0 22 0.60 none Example 10 C61 4 20 0 8 7 0 32 2 22 0.70 none Example 11 C 61 6 17 16 0 0 0 39 0 220.56 present Example 12 C 67 7 10 13 2 1 0 32 0 16 0.51 none Comp. Ex.13 D 71 3 6 18 0 2 0 27 0 11 0.40 none Example 14 D 79 0 6 13 0 2 0 19 01 0.05 present Comp. Ex. 15 D 63 4 13 2 15 3 0 34 0 18 0.53 presentExample 16 D 76 6 2 0 16 0 0 24 0 12 0.52 none Example 17 E 65 2 9 18 42 0 33 0 19 0.57 none Example 18 E 64 6 12 0 18 0 0 36 0 12 0.32 noneExample 19 E 55 12 16 15 0 1 1 43 0 14 0.32 none Example 20 E 76 5 3 3 00 13  11 0 6 0.59 none Comp. Ex. 21 F 67 8 5 17 1 2 0 31 0 23 0.74 noneExample 22 F 60 25 9 0 5 1 0 39 0 26 0.67 none Example 23 F 65 11 16 3 05 0 30 2 25 0.84 none Example 24 F 71 4 9 15 0 1 0 28 0 10 0.36 noneExample 25 G 72 9 0 15 3 1 0 27 0 21 0.78 none Example

TABLE 24 Microstructure Base steel surface layer Grain ¼ thicknessbound- Structure fraction Structure fraction aries Hard Hard and/orExperi- Chemical Bainitic Mar- Tempered Residual phase Residual phaseoxides mental com- Ferrite Bainite ferrite tensite martensite austeniteothers V2 austenite V1 V1/ in Example ponents % % % % % % % % % % V2grains 26 G 45 12 0 0 43 0 0 55 0 33 0.60 present Example 27 G 67 14 314 0 2 0 31 2 31 1.00 none Comp. Ex. 28 G 72 12 3 13 0 0 0 28 0 20 0.72none Example 29 H 70 2 5 21 0 2 0 28 0 16 0.58 none Example 30 H 62 4 104 18 2 0 36 0 27 0.75 none Example 31 H 87 0 3 8 0 2 0 11 1 7 0.61 noneExample 32 I 70 12 0 18 0 0 0 30 0 15 0.51 none Example 33 I 68 18 6 0 44 0 28 1 17 0.60 present Example 34 I 83 5 2 9 1 0 0 17 0 14 0.80 noneExample 35 J 70 7 5 16 0 2 0 28 0 12 0.43 present Example 36 J 56 10 245 0 5 0 39 2 33 0.85 none Example 37 J 70 8 4 15 0 3 0 27 0 18 0.68 noneExample 38 K 65 10 2 17 5 1 0 34 0 24 0.71 none Example 39 K 55 21 13 60 0 5 40 0 34 6.84 none Example 40 K 55 9 21 9 0 6 0 39 2 26 0.67present Example 41 L 73 0 5 19 0 3 0 24 0 16 0.68 none Example 42 L 45 04 0 51 0 0 55 0 41 0.75 none Example 43 L 74 4 10 2 0 0 10  16 0 12 0.72none Comp. Ex. 44 M 87 5 0 8 0 0 0 13 0 7 0.55 none Example 45 M 59 26 67 0 2 0 39 0 22 0.56 none Example 46 M 87 0 0 8 4 1 0 12 1 10 0.83 noneComp. Ex. 47 N 62 13 3 21 0 0 1 37 0 26 0.69 none Example 48 N 51 18 0 031 0 0 49 0 31 0.63 none Example 49 N 31 31 6 24 5 3 0 66 3 49 0.74 noneComp. Ex. 50 O 74 0 8 15 0 3 0 23 1 12 0.54 none Example

TABLE 25 Microstructure Base steel surface layer Grain ¼ thicknessbound- Structure fraction Structure fraction aries Hard Hard and/orExperi- Chemical Bainitic Mar- Tempered Residual phase Residual phaseoxides mental com- Ferrite Bainite ferrite tensite martensite austeniteothers V2 austenite V1 V1/ in Example ponents % % % % % % % % % % V2grains 51 O 76 2 6 14 0 2 0 22 0 2 0.08 none Comp. Ex. 52 O 69 0 9 21 01 0 30 0 17 0.56 none Example 53 O 75 0 8  0 17 0 0 25 0 7 0.28 noneExample 54 P 74 9 2 14 0 1 0 25 0 17 0.66 none Example 55 P 68 10 15  10 6 0 26 2 21 0.79 none Example 56 P 72 10 7 10 1 0 0 28 0 23 0.82 noneExample 57 Q 84 0 4 12 0 0 0 16 0 11 0.66 none Example 58 Q 66 14 8 12 00 0 34 0 25 0.74 none Example 59 Q 58 5 19  0 12 6 0 36 5 28 0.77 noneComp. Ex. 60 R 91 0 0  7 0 2 0 7 0 5 0.68 none Example 61 R 88 3 0  9 00 0 12 0 4 0.37 none Example 62 R 93 0 0  0 7 0 0 7 0 5 0.71 noneExample 63 S 73 3 10 13 0 1 0 26 0 19 0.74 none Example 64 S 71 0 0 24 32 0 27 0 15 0.54 none Example 65 S 73 4 8 15 0 0 0 27 0 12 0.46 noneComp. Ex. 66 T 73 7 2 15 2 0 1 26 0 15 0.59 none Example 67 T 70 22 8  00 0 0 30 0 19 0.62 present Example 68 T 28 21 10 37 0 4 0 68 2 46 0.68none Comp. Ex. 69 U 76 4 7 11 0 2 0 22 0 14 0.62 none Example 70 U 61 34 27 0 5 0 34 3 26 0.77 none Example 71 U 63 14 21  0 0 2 0 35 0 26 0.74present Example 72 V 67 8 3 21 0 1 0 32 0 19 0.60 none Example 73 V 6327 9  0 0 1 0 36 0 26 0.73 none Example 74 V 88 0 0  0 12 0 0 12 0 80.68 none Example 75 W 68 6 3 23 0 0 0 32 0 19 0.60 none Example

TABLE 26 Microstructure Base steel surface layer Grain ¼ thicknessbound- Structure fraction Structure fraction aries Hard Hard and/orExperi- Chemical Bainitic Mar- Tempered Residual phase Residual phaseoxides mental com- Ferrite Bainite ferrite tensite martensite austeniteothers V2 austenite V1 V1/ in Example ponents % % % % % % % % % % V2grains 76 W 80 2 3 14 0 1 0 19 0 0 0.00 none Comp. Ex. 77 W 85 3 1 0 110 0 15 0 7 0.45 present Example 78 X 90 2 2 6 0 0 0 10 0 5 0.45 presentExample 79 X 72 8 4 15 0 1 0 27 0 16 0.58 present Example 80 X 74 6 0 020 0 0 26 0 15 0.57 none Comp. Ex. 81 Y 84 0 4 11 0 1 0 15 0 8 0.55 noneExample 82 Y 52 14 0 0 34 0 0 48 0 25 0.53 none Example 83 Y 73 12 6 9 00 0 27 0 17 0.63 none Example 84 Z 71 8 3 18 0 0 0 29 0 19 0.66 noneExample 85 Z 67 10 5 16 0 2 0 31 0 14 0.45 none Comp. Ex. 86 Z 81 4 0 140 1 0 18 0 14 0.76 none Example 87 AA 72 3 6 16 1 2 0 26 0 15 0.57 noneExample 88 AA 60 0 13 3 22 2 0 38 1 29 0.76 none Example 89 AB 59 11 723 0 0 0 41 0 31 0.75 none Example 90 AB 62 38 0 0 0 0 0 38 0 27 0.70none Example 91 AB 76 15 6 0 0 3 0 21 1 13 0.60 none Example 92 AC 88 02 7 0 3 0 9 0 6 0.70 none Example 93 AC 87 0 3 5 0 5 0 8 2 5 0.63present Example 94 AD 62 8 6 24 0 0 0 38 0 30 0.80 none Example 95 AD 617 8 0 23 1 0 38 0 21 0.56 present Example 96 AE 69 7 3 17 0 1 3 27 0 160.58 none Example 97 AE 55 33 4 0 8 0 0 45 0 33 0.74 none Example 98 AF74 6 4 13 0 2 1 23 1 13 0.56 none Example 99 AF 50 2 6 34 8 0 0 50 0 290.57 none Example 100 AG 68 6 6 18 0 2 0 30 0 21 0.70 none Example

TABLE 27 Microstructure Base steel surface layer Grain ¼ thicknessbound- Structure fraction Structure fraction aries Hard Hard and/orExperi- Chemical Bainitic Mar- Tempered Residual phase Residual phaseoxides mental com- Ferrite Bainite ferrite tensite martensite austeniteothers V2 austenite V1 V1/ in Example ponents % % % % % % % % % % V2grains 101 AG 60 0 9 21 0 0 10 30 0 22 0.73 none Example 102 AH 57 7 525 2 4 0 39 1 22 0.57 none Example 103 AH 60 4 31 5 0 0 0 40 0 34 0.85none Example 104 AI 84 2 0 12 0 2 0 14 2 8 0.57 none Example 105 AI 7121 4 4 0 0 0 29 0 21 0.72 none Example 106 AJ 70 8 5 16 0 1 0 29 0 170.59 none Example 107 AJ 58 13 5 24 0 0 0 42 0 26 0.63 none Example 108AK 56 7 8 26 0 3 0 41 0 28 0.69 present Example 109 AK 54 13 25 5 0 3 043 0 18 0.43 none Example 110 AL 86 5 0 6 0 0 3 11 0 8 0.76 none Example111 AL 76 19 5 0 0 0 0 24 0 16 0.65 none Example 112 AM 63 13 3 19 0 1 135 0 17 0.48 none Example 113 AM 64 5 6 0 24 1 0 35 0 20 0.58 noneExample 114 AM 63 7 14 8 3 5 0 32 2 18 0.55 none Example 115 AM 61 15 1012 0 2 0 37 0 3 0.09 none Comp. Ex. 116 AN 79 5 3 11 0 0 2 19 0 14 0.72none Example 117 AN 61 7 6 23 0 3 0 36 0 28 0.79 none Example 118 AO 815 3 10 0 1 0 18 0 13 0.74 none Example 119 AO 70 7 4 19 0 0 0 30 0 180.60 none Example 120 AP 77 8 4 8 0 1 2 20 0 11 0.56 none Example 121 AP69 16 1 14 0 0 0 31 0 26 0.83 none Example 122 AP 75 18 4 3 0 0 0 25 019 0.76 none Example 123 AQ 83 5 0 10 0 0 2 15 0 9 0.58 present Example124 AQ 83 6 1 10 0 0 0 17 0 9 0.50 none Example 125 AR 87 4 2 7 0 0 0 130 6 0.45 present Example

TABLE 28 Microstructure ¼ thickness Base steel surface layer Structurefraction Structure fraction Grain Hard Hard boundaries Exper- ChemicalFer- Bainitic Marten- Tempered Residual phase Residual phase and/orimental com- rite Bainite ferrite site martensite austenite others V2austenite V1 V1/ oxides in Example ponents % % % % % % % % % % V2 grains126 AR 73 7 3 15 0 2 0 25 0 19 0.77 none Example 127 AS 75 2 8 15 0 0 025 0 17 0.67 none Example 128 AS 61 9 16 14 0 0 0 39 0 32 0.82 noneExample 129 AT 80 2 3 14 0 0 1 19 0 12 0.64 present Example 130 AT 88 42 0 6 0 0 12 0 7 0.60 none Example 131 AU 87 2 0 11 0 0 0 13 0 9 0.72none Example 132 AU 80 5 3 12 0 0 0 20 0 19 0.95 none Comp. Ex. 133 AU86 5 4 0 0 5 0 9 1 7 0.83 none Example 134 AU 88 3 1 7 0 1 0 11 0 7 0.68none Example 135 AV 79 0 5 13 0 3 0 18 0 12 0.64 none Example 136 AV 654 10 19 2 0 0 35 0 27 0.78 none Comp. Ex. 137 AV 61 13 17 4 0 5 0 34 326 0.75 none Example 138 AW 67 11 4 16 0 1 1 31 0 22 0.71 none Example139 AW 63 13 8 0 0 0 16  21 0 14 0.66 none Comp. Ex. 140 AW 60 23 13 0 04 0 36 2 23 0.65 present Example 141 AX 61 5 6 23 2 3 0 36 0 27 0.75none Example 142 AX 64 11 6 18 0 1 0 35 0 26 0.73 none Example 143 AY 534 16 25 0 2 0 45 1 28 0.62 present Example 144 AY 54 6 34 0 0 6 0 40 022 0.55 none Example 145 AZ 72 5 9 12 0 0 2 26 0 20 0.75 none Example146 AZ 74 5 6 15 0 0 0 26 0 20 0.76 none Example 147 BA 75 3 5 15 0 2 023 0 18 0.78 none Example 148 BA 56 10 5 21 7 1 0 43 0 23 0.54 presentExample 149 BB 56 8 7 26 0 3 0 41 0 27 0.66 none Example 150 BB 70 5 816 0 1 0 29 0 19 0.65 none Comp. Ex.

TABLE 29 Microstructure ¼ thickness Base steel surface layer Structurefraction Structure fraction Grain Hard Hard boundaries Exper- ChemicalFer- Bainitic Marten- Tempered Residual phase Residual phase and/orimental com- rite Bainite ferrite site martensite austenite others V2austenite V1 V1/ oxides in Example ponents % % % % % % % % % % V2 grains151 BB 65 8 20 3 0 4 0 31 0 18 0.58 none Example 152 BB 66 11 14 9 0 0 034 0 13 0.38 none Example 153 BC 86 4 0 8 0 0 2 12 0 9 0.75 none Example154 BC 66 13 6 4 5 5 1 28 1 22 0.78 none Example 155 BC 67 9 3 21 0 0 033 0 24 0.74 none Example 156 BC 79 10 8 0 0 3 0 18 0 14 0.76 presentExample 157 BC 82 4 3 11 0 0 0 18 0 17 0.97 none Comp. Ex. 158 BD 80 5 011 0 1 3 16 1 12 0.76 none Example 159 BD 80 6 0 14 0 0 0 20 0 15 0.77none Example 160 BE 77 3 4 14 0 2 0 21 0 14 0.67 none Example 161 BE 850 4 9 0 2 0 13 0 8 0.62 none Example 162 BF 64 13 7 13 0 3 0 33 0 180.55 none Example 163 BF 61 5 7 24 0 3 0 36 0 28 0.77 none Example 164BF 63 1 27 4 0 5 0 32 2 17 0.53 none Example 165 BF 63 3 21 0 0 13  0 243 13 0.56 none Comp. Ex. 166 BG 87 0 4 7 0 2 0 11 0 4 0.35 none Example167 BG 41 5 10 0 42 2 0 57 0 34 0.60 none Example 168 BG 80 3 6 11 0 0 020 0 1 0.06 none Comp. Ex. 169 BG 71 2 6 19 0 2 0 27 0 14 0.52 noneExample 170 BH 65 3 7 19 5 0 1 34 0 22 0.65 none Example 171 BH 54 5 1425 0 2 0 44 0 33 0.75 none Comp. Ex. 172 BH 58 6 27 3 0 6 0 36 2 29 0.80none Example 173 BH 54 13 23 5 0 5 0 41 0 34 0 83 none Example 174 BI 850 5 8 0 2 0 13 0 7 0.57 present Example 175 BI 75 2 13 0 5 5 0 20 0 90.46 none Example

TABLE 30 Microstructure ¼ thickness Base steel surface layer Structurefraction Structure fraction Hard Hard Grains Exper- Chemical Fer-Bainitic Marten- Tempered Residual phase Residual phase and/or imentalcom- rite Bainite ferrite site martensite austenite others V2 austeniteV1 V1/ oxides in Example ponents % % % % % % % % % % V2 grains 176 BJ 834 2 11  0 0 0 17 0 10 0.60 none Example 177 BJ 63 9 16 0 0 0 12  25 0 210.83 none Comp. Ex. 178 BJ 83 3 4 8 0 2 0 15 0 10 0.64 none Example 179BK 86 0 0 12  0 2 0 12 0 6 0.49 none Example 180 BK 64 14 7 15  0 0 0 360 31 0.85 none Example 181 BL 78 3 3 16  0 0 0 22 0 17 0.78 presentExample 182 BL 61 8 6 3 21 1 0 38 0 33 0.88 none Example 183 BL 78 5 6 90 2 0 20 0 11 0.55 none Comp. Ex. 184 BL 68 20 10 2 0 0 0 32 0 20 0.61none Example 185 BM 79 0 8 11  0 2 0 19 1 9 0.48 none Example 186 BM 900 0 0 0 0 10   0 0 0 0.46 none Comp. Ex. 187 BM 76 0 13 5 0 6 0 18 0 70.37 none Example 188 BN 86 5 2 7 0 0 0 14 0 8 0.54 none Example 189 BN73 10 0 0 17 0 0 27 0 19 0.69 present Example 190 BO 98 0 1 0 0 0 1  1 00 0.00 none Comp. Ex. 191 BP 47 7 6 37  0 3 0 50 0 38 0.75 none Comp.Ex. 192 BQ 71 8 0 0 0 0 21  8 0 6 0.75 none Comp. Ex. 193 BR Experimentstopped due to occurrence of cracking of slab during heating in hotrolling step Comp. Ex. 194 BS 84 0 2 0 0 0 14   2 0 0 0.00 none Comp.Ex. 195 BT Experiment stopped due to occurrence of cracking of slabduring heating in hot rolling step Comp. Ex. 196 BU Experiment stoppeddue to occurrence of cracking of slab during hot rolling in hot rollingstep Comp. Ex. 197 BV 70 11 4 14  0 1 0 29 0 19 0.67 none Comp. Ex. 198BW Experiment stopped due to occurrence of cracking of slab duringtransportation after casting of slab Comp. Ex. 199 BX 68 6 8 17  0 1 031 0 24 0.79 none Comp. Ex. 200 BY 60 4 7 26  0 3 0 37 0 23 0.62 noneComp. Ex. 201 A 59 8 12 17  0 4 0 38 0 18 0.47 none Comp. Ex.

TABLE 31 Plated layer ζ Phase δ1 Phase Base steel sheet BoundaryOccupancy Boundary Average Average surface ratio of ζ surface thicknessgrain size Maximum Content occupancy grain in which occupancy Plated ofrefined of ferrite size of Experimental Chemical Fe Al ratio oxidespresent ratio amount layer phase oxide Example components % % % % % g/m2μm μm μm 1 A 3.6 0.19 51 0 0 61 2.4 1.6 0.02 Example 2 A 8.2 0.12 51 049 56 2.7 0.8 0.02 Comp. Ex. 3 A 2.5 0.20 59 0 0 67 2.4 0.6 0.04 Example4 A 1.9 0.24 57 0 0 56 2.7 0.7 0.1 Example 5 B 2.8 0.23 40 0 0 74 3.70.6 0.1 Example 6 B 3.2 0.40 40 4 0 69 3.5 0.3 0.2 Example 7 B 0.9 0.4335 0 0 60 3.4 0.4 0.1 Example 8 B 0.7 0.18 42 0 0 72 0.9 1.6 0.1 Example9 C 2.8 0.26 46 6 0 58 2.3 0.4 0.2 Example 10 C 0.9 0.18 52 6 0 67 1.60.5 0.3 Example 11 C 1.7 0.20 41 5 0 63 2.2 0.4 0.3 Example 12 C 0.10.54  6 0 0 58 2.2 0.3 0.1 Comp. Ex. 13 D 1.6 0.23 51 0 0 68 3.0 0.3 0.1Example 14 D 2.8 0.18 69 0 0 67 3.7 0.4 0.02 Comp. Ex. 15 D 2.2 0.31 410 0 65 2.9 0.4 0.04 Example 16 D 2.0 0.32 53 0 0 66 2.6 1.8 0.04 Example17 E 2.0 0.23 65 0 0 70 2.3 1.5 0.02 Example 18 E 1.6 0.22 37 5 0 70 3.00.3 0.3 Example 19 E 1.9 0.19 50 0 0 66 2.5 0.4 0.1 Example 20 E 2.40.17 56 0 0 57 2.4 0.4 0.1 Comp. Ex. 21 F 2.0 0.25 49 9 0 68 2.8 0.4 0.3Example 22 F 1.5 0.37 26 0 0 68 3.1 0.3 0.1 Example 23 F 1.2 0.29 50 100 64 1.9 0.4 0.5 Example 24 F 3.4 0.16 63 0 0 64 4.2 0.3 0.01 Example 25G 2.6 0.34 49 0 0 71 2.9 0.3 0.1 Example 26 G 2.6 0.33 42 0 0 61 3.3 0.30.04 Example 27 G 2.0 0.30 39 0 0 65 3.2 0.3 0.04 Comp. Ex. 28 G 1.80.34 49 0 0 56 3.6 0.3 0.02 Example 29 H 2.1 0.22 48 4 0 70 2.3 0.4 0.2Example 30 H 1.4 0.29 17 10 0 64 1.0 0.5 0.2 Example 31 H 2.0 0.42 58 00 61 2.4 0.3 0.1 Example 32 I 2.9 0.31 56 19 0 67 3.5 0.4 0.4 Example 33I 4.2 0.16 88 28 3 75 1.8 0.6 0.1 Example 34 I 2.5 0.31 46 0 0 58 2.51.3 0.04 Example 35 J 2.5 0.26 51 8 0 72 2.9 0.3 0.3 Example 36 J 2.00.29 42 0 0 54 2.5 0.4 0.1 Example 37 J 1.1 0.25 29 9 0 66 0.8 1.9 0.4Example 38 K 2.1 0.24 40 0 0 69 1.9 0.3 0.03 Example 39 K 1.9 0.25 50 00 71 2.1 0.4 0.1 Example 40 K 2.6 0.21 54 6 0 55 2.9 0.2 0.2 Example 41L 2.3 0.26 62 8 0 56 2.6 0.3 0.3 Example 42 L 2.1 0.32 51 0 0 65 2.3 0.30.1 Example 43 L 3.2 0.46 40 0 0 57 3.0 0.3 0.03 Comp. Ex. 44 M 2.9 0.2051 0 0 65 3.4 0.3 0.02 Example 45 M 2.0 0.37 31 0 0 57 3.3 0.3 0.03Example 46 M 3.0 0.27 62 0 0 66 2.8 0.4 0.1 Comp. Ex. 47 N 3.0 0.16 65 90 64 3.5 0.3 0.5 Example 48 N 3.2 0.33 60 7 0 61 3.3 0.2 0.3 Example 49N 3.6 0.31 45 0 0 63 3.1 0.3 0.02 Comp. Ex. 50 O 2.0 0.27 55 0 0 62 1.90.4 0.02 Example

TABLE 32 Plated layer ζ Phase δ1 Phase Base steel sheet BoundaryOccupancy Boundary Average Average surface ratio of ζ surface thicknessgrain size Maximum Content occupancy grain in which occupancy Plated ofrefined of ferrite size Experimental Chemical Fe Al ratio oxides presentratio amount layer phase of oxide Example components % % % % % g/m2 μmμm μm 51 O 1.3 0.27 40 4 0 63 1.0 0.5 0.2 Comp. Ex. 52 O 1.7 0.30 33 0 062 1.8 0.3 0.1 Example 53 O 1.0 0.09 31 0 0 60 1.8 0.6 0.1 Example 54 P2.0 0.20 46 0 0 74 2.3 1.4 0.1 Example 55 P 1.3 0.22 26 7 0 65 0.3 0.90.4 Example 56 P 0.6 0.29 21 0 0 66 2.1 0.5 0.1 Example 57 Q 1.3 0.22 420 0 62 2.4 0.4 0.1 Example 58 Q 1.5 0.31 48 0 0 70 2.2 0.4 0.1 Example59 Q 1.6 0.25 44 8 0 74 2.0 0.5 0.3 Comp. Ex. 60 R 3.7 0.22 60 0 0 752.1 0.4 0.1 Example 61 R 2.1 0.19 55 0 0 68 2.0 0.4 0.1 Example 62 R 3.10.17 63 4 0 64 2.9 0.4 0.2 Example 63 S 3.2 0.27 48 0 0 68 2.3 0.3 0.1Example 64 S 2.3 0.37 33 0 0 58 1.9 0.5 0.1 Example 65 S 2.7 0.27 36 0 0152  1.8 0.4 0.1 Comp. Ex. 66 T 2.7 0.29 53 4 0 56 2.4 0.4 0.2 Example67 T 3.0 0.27 51 0 0 56 3.0 1.5 0.02 Example 68 T 1.2 0.22 32 0 0 75 2.60.5 0.1 Comp. Ex. 69 U 2.4 0.23 54 0 0 58 1.8 0.5 0.1 Example 70 U 1.80.27 61 4 0 57 1.7 0.3 0.2 Example 71 U 2.3 0.20 46 0 0 66 1.1 0.5 0.02Example 72 V 1.4 0.19 45 0 0 74 3.9 0.5 0.03 Example 73 V 1.2 0.45 37 00 56 2.2 0.6 0.04 Example 74 V 1.6 0.31 35 0 0 68 2.0 0.5 0.04 Example75 W 1.6 0.27 50 0 0 72 1.9 0.4 0.1 Example 76 W 7.1 0.14 14 7 81 5814.1 0.2 0.4 Comp. Ex. 77 W 2.7 0.25 45 0 0 63 2.7 0.4 0.1 Example 78 X1.4 0.27 48 5 0 66 2.6 0.4 0.3 Example 79 X 2.0 0.31 46 0 0 69 3.1 0.50.1 Example 80 X 2.2 0.20 51 5 0 75 2.6 0.5 0.4 Comp. Ex. 81 Y 2.8 0.2159 0 0 59 2.1 0.5 0.1 Example 82 Y 3.3 0.13 67 0 0 70 2.4 0.5 0.1Example 83 Y 2.4 0.16 54 6 0 60 1.4 0.8 0.3 Example 84 Z 1.9 0.28 46 0 071 2.7 0.6 0.04 Example 85 Z 2.6 0.23 63 0 0 70 2.3 0.5 1.0 Comp. Ex. 86Z 1.9 0.16 56 4 0 58 2.9 0.5 0.2 Example 87 AA 1.8 0.30 55 0 0 63 2.12.5 0.02 Example 88 AA 1.8 0.28 41 7 0 58 1.6 0.6 0.4 Example 89 AB 2.40.20 54 0 0 66 4.3 0.4 0.04 Example 90 AB 2.1 0.75 28 0 0 65 4.6 0.40.02 Example 91 AB 1.9 0.26 40 0 0 66 0.5 0.7 0.1 Example 92 AC 1.7 0.1840 4 0 59 1.7 0.5 0.2 Example 93 AC 1.6 0.20 55 0 0 57 1.9 0.5 0.1Example 94 AD 3.8 0.23 60 0 0 57 2.5 0.3 0.1 Example 95 AD 2.2 0.22 58 90 67 2.6 0.3 0.5 Example 96 AE 2.6 0.27 39 0 0 65 2.5 2.4 0.02 Example97 AE 3.0 0.30 49 4 0 64 2.5 0.4 0.3 Example 98 AF 2.1 0.22 54 5 0 722.4 0.5 0.3 Example 99 AF 2.1 0.19 50 0 0 70 2.0 0.4 0.1 Example 100 AG1.6 0.24 41 0 0 59 1.9 0.5 0.1 Example

TABLE 33 Plated layer ζ Phase Occupancy δ1 Phase Boundary ratio ofBoundary Base steel sheet surface ζ grain in surface Average Averagegrain Content occupancy which oxides occupancy Plated thickness of sizeof ferrite Maximum Experimental Chemical Fe Al ratio present ratioamount refined layer phase size of oxide Example components % % % % %g/m2 μm μm μm 101 AG 2.6 0.20 69 0 0 69 2.8 0.4 0.1 Example 102 AH 2.80.21 56 0 0 72 3.0 0.5 0.03 Example 103 AH 2.9 0.29 48 0 0 72 2.3 0.50.04 Example 104 AI 2.1 0.25 52 7 0 68 2.8 0.4 0.2 Example 105 AI 1.70.29 35 0 0 62 2.3 0.5 0.04 Example 106 AJ 2.3 0.23 40 0 0 69 3.1 1.50.02 Example 107 AJ 3.6 0.13 80 0 0 64 3.2 0.6 0.1 Example 108 AK 2.20.19 63 4 0 71 2.8 0.5 0.2 Example 109 AK 2.0 0.16 61 0 0 76 2.3 0.4 0.1Example 110 AL 4.2 0.26 61 5 5 57 4.4 0.6 0.4 Example 111 AL 3.1 0.30 380 0 67 4.0 0.4 0.1 Example 112 AM 1.8 0.21 56 0 0 68 2.7 0.5 0.1 Example113 AM 3.1 0.18 51 0 0 57 2.1 0.4 0.1 Example 114 AM 2.2 0.24 50 0 0 732.4 0.4 0.1 Example 115 AM 1.6 0.20 45 0 0 70 2.7 0.5 0.1 Comp. Ex. 116AN 2.6 0.30 53 0 0 70 2.9 0.6 0.1 Example 117 AN 2.0 0.23 53 5 0 63 2.20.4 0.3 Example 118 AO 2.3 0.44 57 0 0 65 2.3 0.4 0.04 Example 119 AO2.8 0.34 33 0 0 72 2.9 0.5 0.1 Example 120 AP 2.1 0.23 44 0 0 61 3.7 0.60.1 Example 121 AP 2.5 0.18 48 0 0 73 2.7 0.5 0.1 Example 122 AP 2.60.35 39 0 0 66 2.9 0.5 0.03 Example 123 AQ 2.4 0.28 67 0 0 71 3.6 0.40.1 Example 124 AQ 2.4 0.30 31 0 0 69 3.4 0.5 0.1 Example 125 AR 1.70.26 37 0 0 71 3.5 2.4 0.01 Example 126 AR 2.5 0.24 57 0 0 67 3.3 0.50.1 Example 127 AS 2.5 0.26 49 0 0 58 2.6 0.4 0.1 Example 128 AS 2.50.35 43 0 0 56 2.0 0.4 0.02 Example 129 AT 1.1 0.18 42 5 0 63 3.1 0.60.3 Example 130 AT 4.4 0.38 69 0 0 75 2.7 0.4 0.04 Example 131 AU 2.10.35 43 0 0 58 2.7 0.5 0.1 Example 132 AU 2.4 0.26 47 6 0 67 2.5 0.6 0.5Comp. Ex. 133 AU 1.3 0.22 42 0 0 59 0.7 0.8 0.1 Example 134 AU 1.3 0.1746 0 0 66 3.2 0.5 0.1 Example 135 AV 1.8 0.21 50 0 0 71 2.6 0.7 0.04Example 136 AV 1.8 0.19 55 9 0  8 2.0 0.5 0.4 Comp. Ex. 137 AV 2.2 0.3457 0 0 71 2.0 0.5 0.1 Example 138 AW 2.0 0.25 36 0 0 60 2.8 0.5 0.1Example 139 AW 2.3 0.35 39 7 0 55 3.6 0.5 0.4 Comp. Ex. 140 AW 1.8 0.1846 8 0 60 3.8 0.5 0.6 Example 141 AX 1.7 0.20 37 0 0 58 2.6 0.6 0.1Example 142 AX 3.3 0.40 51 8 0 75 3.2 0.4 0.4 Example 143 AY 2.3 0.19 440 0 57 2.4 0.6 0.03 Example 144 AY 1.4 0.16 47 0 0 70 2.1 0.4 0.04Example 145 AZ 1.5 0.32 43 0 0 72 2.4 0.5 0.1 Example 146 AZ 1.9 0.22 477 0 61 2.0 0.4 0.5 Example 147 BA 1.5 0.24 32 0 0 63 1.8 0.4 0.1 Example148 BA 1.8 0.16 40 0 0 62 2.5 0.5 0.1 Example 149 BB 2.1 0.26 45 9 0 712.9 0.5 0.3 Example 150 BB 0.4 1.08 11 0 0 64 2.8 0.4 0.1 Comp. Ex.

TABLE 34 Plated layer ζ Phase Occupancy δ1 Phase Boundary ratio ofBoundary Base steel sheet surface ζ grain in surface Average Averagegrain Content occupancy which oxides occupancy Plated thickness of sizeof ferrite Maximum Experimental Chemical Fe Al ratio present ratioamount refined layer phase size of oxide Example components % % % % %g/m2 μm μm μm 151 BB 3.0 0.35 53 0 0 56 2.7 0.4 0.1 Example 152 BB 4.50.10 80 9 2 66 2.7 0.3 0.4 Example 153 BC 2.2 0.41 38 0 0 65 3.9 0.70.03 Example 154 BC 1.3 0.19 52 0 0 72 3.5 0.7 0.1 Example 155 BC 2.60.12 74 0 0 61 4.3 0.4 0.04 Example 156 BC 2.4 0.28 44 0 0 56 4.0 6.40.1 Example 157 BC 1.9 0.26 38 0 0 70 4.2 0.4 0.1 Comp. Ex. 158 BD 4.50.24 63 0 0 72 4.9 0.6 0.1 Example 159 BD 2.9 0.31 67 0 0 62 4.9 2.50.02 Example 160 BE 1.9 0.20 50 0 0 59 3.0 0.4 0.1 Example 161 BE 1.80.35 35 0 0 59 3.0 0.5 0.1 Example 162 BF 1.3 0.24 33 0 0 57 2.4 0.4 0.1Example 163 BF 1.3 0.23 48 0 0 60 0.5 0.8 0.1 Example 164 BF 3.5 0.25 860 0 71 2.5 0.4 0.1 Example 165 BF 1.7 0.25 41 5 0 71 2.3 0.5 0.3 Comp.Ex. 166 BG 1.5 0.18 56 0 0 68 2.2 0.5 0.1 Example 167 BG 1.2 0.34 32 9 061 1.7 0.5 0.2 Example 168 BG 1.3 0.30 51 0 0 59 2.2 0.5 0.1 Comp. Ex.169 BG 1.7 0.17 52 10 0 57 1.9 0.4 0.3 Example 170 BH 2.5 0.24 42 0 0 582.3 0.4 0.03 Example 171 BH 0.1 0.36  5 0 0 70 <0.1  (3.4) (<0.01) Comp.Ex. 172 BH 4.1 0.19 73 10 11 68 1.9 0.5 0.5 Example 173 BH 2.1 0.40 51 00 71 2.1 0.5 0.04 Example 174 BI 0.9 0.25 44 0 0 73 1.8 0.5 0.02 Example175 BI 2.4 0.26 62 0 0 58 2.2 0.4 0.02 Example 176 BJ 3.2 0.18 61 0 0 583.0 0.5 0.04 Example 177 BJ 1.6 0.23 54 10 0 56 2.4 0.5 0.5 Comp. Ex.178 BJ 1.8 0.22 4 0 0 62 2.2 0.5 0.1 Example 179 BK 1.7 0.21 48 0 0 593.7 0.4 0.1 Example 180 BK 1.7 0.22 40 9 0 62 2.7 0.5 0.3 Example 181 BL3.2 0.21 65 0 0 59 2.7 0.5 0.1 Example 182 BL 2.9 0.39 50 0 0 68 2.1 0.40.02 Example 183 BL 5.8 0.30 67 0 25 70 2.8 0.3 0.1 Comp. Ex. 184 BL 1.90.28 33 0 0 70 0.5 0.8 0.03 Example 185 BM 1.5 0.23 49 0 0 68 1.9 0.50.04 Example 186 BM 2.3 0.22 49 0 0 67 1.7 0.4 0.1 Comp. Ex. 187 BM 1.50.19 31 0 0 58 1.9 0.5 0.1 Example 188 BN 3.7 0.23 66 4 0 60 4.1 0.4 0.3Example 189 BN 3.0 0.31 56 5 0 73 4.0 0.6 0.4 Example 190 BO 1.9 0.22 490 0 68 2.3 0.5 0.1 Comp. Ex. 191 BP 2.6 0.37 50 0 0 66 2.2 0.5 0.1 Comp.Ex. 192 BQ 4.0 0.42 54 0 0 70 4.8 0.5 0.1 Comp. Ex. 193 BR Experimentstopped due to occurrence of cracking of slab during heating in hotrolling step Comp. Ex. 194 BS 1.2 0.20 34 0 0 76 2.9 0.6 0.03 Comp. Ex.195 BT Experiment stopped due to occurrence of cracking of slab duringheating in hot rolling step Comp. Ex. 196 BU Experiment stopped due tooccurrence of cracking of slab during hot rolling in hot rolling stepComp. Ex. 197 BV 1.1 0.22 39 4 0 60 2.5 0.7 0.4 Comp. Ex. 198 BWExperiment stopped due to occurrence of cracking of slab duringtransportation after casting of slab Comp. Ex. 199 BX 2.1 0.23 59 0 0 712.3 0.5 0.1 Comp. Ex. 200 BY 1.9 0.18 47 0 0 55 2.9 0.6 0.03 Comp. Ex.201 A 6.6 0.19 65 0 30 65 7.4 0.6 0.10 Comp. Ex.

TABLE 35 Tensile properties Bendability Maximum Total Minimum Yieldstrength tensile Elongation Hole TS^(0.5) × bending ExperimentalChemical Thickness t YS strength TS El expansibility λ El × radius rExample components mm MPa MPa % % λ^(0.5) mm r/t  1 A 1.5 454 748 24 372.99E+06 1.5 1.0  2 A 1.6 454 732 26 33 2.96E+06 1.5 0.9  3 A 2.0 322569 30 86 3.78E+06 3.5 1.8  4 A 1.5 371 693 27 40 3.12E+06 1.5 1.0  5 B1.5 349 613 32 53 3.54E+06 3.0 2.0  6 B 1.6 316 619 31 50 3.38E+06 2.01.3  7 B 1.7 341 608 30 48 3.12E+06 1.0 0.6  8 B 1.2 342 553 33 543.15E+06 2.0 1.7  9 C 1.5 510 935 20 22 2.68E+06 1.0 0.7 10 C 1.2 575820 23 33 3.10E+06 1.0 0.8 11 C 1.3 551 890 18 38 2.95E+06 1.5 1.2 12 C1.7 410 748 23 39 2.94E+06 2.5 1.5 13 D 2.8 347 696 31 23 2.73E+06 4.51.6 14 D 1.3 357 699 29 33 3.08E+06 1.0 0.8 15 D 1.4 432 622 29 613.51E+06 2.5 1.8 16 D 1.2 342 609 30 73 3.85E+06 1.0 0.8 17 E 1.5 5911015 15 41 3.11E+06 1.0 0.7 18 E 1.8 569 826 22 51 3.73E+06 2.0 1.1 19 E1.2 583 913 17 28 2.48E+06 1.5 1.3 20 E 1.6 359 603 16 27 1.23E+06 2.01.3 21 F 1.5 505 880 17 47 3.04E+06 1.0 0.7 22 F 1.6 429 633 26 873.86E+06 1.5 0.9 23 F 1.2 488 755 24 31 2.77E+06 1.0 0.8 24 F 1.3 373727 24 35 2.78E+06 1.0 0.8 25 G 1.3 429 833 20 39 3.00E+06 1.5 1.2Fatigue resistance Fatigue limit Experimental DL Plating Spot CorrosionChipping IR90° V Example MPa DL/TS adhesion weldability resistanceProperties bending powdering  1 373 0.50 ∘ ∘ ∘ ∘ ∘ Example  2 333 0.45 x∘ ∘ x x Comp. Ex.  3 253 0.44 ∘ ∘ ∘ ∘ ∘ Example  4 319 0.46 ∘ ∘ ∘ ∘ ∘Example  5 300 0.49 ∘ ∘ ∘ ∘ ∘ Example  6 324 0.52 ∘ ∘ ∘ ∘ ∘ Example  7333 0.55 ∘ ∘ ∘ ∘ ∘ Example  8 284 0.51 ∘ ∘ ∘ ∘ ∘ Example  9 418 0.45 ∘ ∘∘ ∘ ∘ Example 10 469 0.57 ∘ ∘ ∘ ∘ ∘ Example 11 485 0.54 ∘ ∘ ∘ ∘ ∘Example 12 345 0.46 x ∘ ∘ ∘ ∘ Comp. Ex. 13 288 0.41 ∘ ∘ ∘ ∘ ∘ Example 14201 0.29 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 15 301 0.48 ∘ ∘ ∘ ∘ ∘ Example 16 323 0.53 ∘∘ ∘ ∘ ∘ Example 17 498 0.49 ∘ ∘ ∘ ∘ ∘ Example 18 449 0.54 ∘ ∘ ∘ ∘ ∘Example 19 385 0.42 ∘ ∘ ∘ ∘ ∘ Example 20 324 0.54 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 21445 0.51 ∘ ∘ ∘ ∘ ∘ Example 22 299 0.47 ∘ ∘ ∘ ∘ ∘ Example 23 405 0.54 ∘ ∘∘ ∘ ∘ Example 24 318 0.44 ∘ ∘ ∘ ∘ ∘ Example 25 407 0.49 ∘ ∘ ∘ ∘ ∘Example

TABLE 36 Tensile properties Bendability Maximum Total Minimum Yieldstrength tensile Elongation Hole TS^(0.5) × bending ExperimentalChemical Thickness t YS strength TS El expansibility λ El × radius rExample components mm MPa MPa % % λ^(0.5) mm r/t 26 G 1.3 759 985 16 383.05E+06 1.5 1.2 27 G 1.5 516 873 22 25 2.84E+06 3.5 2.3 28 G 1.2 462818 23 22 2.52E+06 1.5 1.3 29 H 1.3 427 772 21 40 2.85E+06 2.0 1.5 30 H1.7 573 877 20 45 3.48E+06 2.5 1.5 31 H 2.4 405 852 24 24 2.92E+06 2.00.8 32 I 1.3 411 742 20 63 3.21E+06 2.0 1.5 33 I 1.5 420 675 27 433.10E+06 2.0 1.3 34 I 1.5 367 717 28 30 2.94E+06 1.0 0.7 35 J 2.0 510949 20 19 2.55E+06 2.0 1.0 36 J 1.6 522 846 21 32 2.92E+06 1.0 0.6 37 J1.7 541 953 19 24 2.74E+06 1.0 0.6 38 K 1.3 693 1111 15 28 2.94E+06 1.00.8 39 K 1.8 456 737 26 40 3.29E+06 2.5 1.4 40 K 1.9 632 1022 16 353.09E+06 1.0 0.5 41 L 1.3 531 976 17 22 2.43E+06 1.0 0.8 42 L 1.4 8281030 16 44 3.51E+06 1.0 0.7 43 L 1.4 353 601 21 20 1.38E+06 2.0 1.4 44 M1.5 338 748 25 32 2.89E+06 2.0 1.3 45 M 1.5 439 700 28 44 3.44E+06 2.01.3 46 M 2.0 393 784 22 40 3.05E+06 4.5 2.3 47 N 1.5 508 832 23 313.07E+06 1.0 0.7 48 N 1.7 631 801 21 60 3.69E+06 2.0 1.2 49 N 2.0 7671128 9 30 1.87E+06 1.5 0.8 50 O 1.5 440 771 24 30 2.81E+06 2.0 1.3Fatigue resistance Fatigue limit Experimental DL Plating Spot CorrosionChipping IR90° V Example MPa DL/TS adhesion weldability resistanceProperties bending powdering 26 514 0.52 ∘ ∘ ∘ ∘ ∘ Example 27 484 0.55 ∘∘ ∘ ∘ ∘ Comp. Ex. 28 390 0.48 ∘ ∘ ∘ ∘ ∘ Example 29 385 0.50 ∘ ∘ ∘ ∘ ∘Example 30 553 0.63 ∘ ∘ ∘ ∘ ∘ Example 31 351 0.41 ∘ ∘ ∘ ∘ ∘ Example 32356 0.48 ∘ ∘ ∘ ∘ ∘ Example 33 359 0.53 ∘ ∘ ∘ ∘ ∘ Example 34 347 0.48 ∘ ∘∘ ∘ ∘ Example 35 388 0.41 ∘ ∘ ∘ ∘ ∘ Example 36 476 0.56 ∘ ∘ ∘ ∘ ∘Example 37 439 0.46 ∘ ∘ ∘ ∘ ∘ Example 38 598 0.54 ∘ ∘ ∘ ∘ ∘ Example 39357 0.48 ∘ ∘ ∘ ∘ ∘ Example 40 538 0.53 ∘ ∘ ∘ ∘ ∘ Example 41 469 0.48 ∘ ∘∘ ∘ ∘ Example 42 428 0.42 ∘ ∘ ∘ ∘ ∘ Example 43 297 0.49 ∘ ∘ ∘ ∘ ∘ Comp.Ex. 44 328 0.44 ∘ ∘ ∘ ∘ ∘ Example 45 314 0.45 ∘ ∘ ∘ ∘ ∘ Example 46 3590.46 x ∘ ∘ ∘ ∘ Comp. Ex. 47 435 0.52 ∘ ∘ ∘ ∘ ∘ Example 48 438 0.55 ∘ ∘ ∘∘ ∘ Example 49 477 0.42 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 50 365 0.47 ∘ ∘ ∘ ∘ ∘Example

TABLE 37 Tensile properties Bendability Maximum Total Minimum Yieldstrength tensile Elongation Hole TS^(0.5) × bending ExperimentalChemical Thickness t YS strength TS El expansibility λ El × radius rExample components mm MPa MPa % % λ^(0.5) mm r/t 51 O 1.3 369 737 20 482.77E+06 1.0 0.8 52 O 1.8 401 810 24 33 3.18E+06 1.5 0.8 53 O 1.3 472748 26 44 3.53E+06 1.5 1.2 54 P 1.5 380 683 23 62 3.23E+06 1.5 1.0 55 P1.5 456 769 27 23 2.76E+06 1.5 1.0 56 P 1.6 418 708 25 35 2.79E+06 2.01.3 57 Q 1.3 439 827 22 31 2.91E+06 1.5 1.2 58 Q 1.9 431 694 27 423.20E+06 2.0 1.1 59 Q 1.7 467 692 26 56 3.54E+06 3.5 2.1 60 R 0.9 287640 24 67 3.18E+06 1.0 1.1 61 R 1.3 291 636 33 31 2.95E+06 2.0 1.5 62 R1.3 275 593 29 75 3.63E+06 2.5 1.9 63 S 1.5 571 974 17 32 2.92E+06 1.00.7 64 S 1.4 528 1050 15 26 2.60E+06 1.0 0.7 65 S 1.6 422 860 22 272.88E+06 2.0 1.3 66 T 1.5 479 911 21 26 3.11E+06 2.0 1.3 67 T 1.6 378607 34 55 3.77E+06 2.0 1.3 68 T 1.3 663 1006  7  8 6.32E+05 3.5 2.7 69 U1.5 396 749 25 34 2.99E+06 1.5 1.0 70 U 1.2 511 960 19 18 2.40E+06 1.00.8 71 U 1.6 406 640 31 43 3.29E+06 1.0 0.6 72 V 1.5 405 714 28 292.88E+06 2.5 1.7 73 V 2.0 342 562 33 72 3.73E+06 1.0 0.5 74 V 1.2 314598 31 49 3.17E+06 1.0 0.8 75 W 1.5 398 772 24 32 2.91E+06 1.5 1.0Fatigue resistance Fatigue limit Experimental DL Plating Spot CorrosionChipping IR90° V Example MPa DL/TS adhesion weldability resistanceProperties bending powdering 51 199 0.27 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 52 365 0.45∘ ∘ ∘ ∘ ∘ Example 53 340 0.45 ∘ ∘ ∘ ∘ ∘ Example 54 313 0.46 ∘ ∘ ∘ ∘ ∘Example 55 293 0.38 ∘ ∘ ∘ ∘ ∘ Example 56 385 0.54 ∘ ∘ ∘ ∘ ∘ Example 57399 0.48 ∘ ∘ ∘ ∘ ∘ Example 58 358 0.52 ∘ ∘ ∘ ∘ ∘ Example 59 378 0.55 ∘ ∘∘ ∘ ∘ Comp. Ex. 60 288 0.45 ∘ ∘ ∘ ∘ ∘ Example 61 270 0.42 ∘ ∘ ∘ ∘ ∘Example 62 292 0.49 ∘ ∘ ∘ ∘ ∘ Example 63 521 0.53 ∘ ∘ ∘ ∘ ∘ Example 64425 0.40 ∘ ∘ ∘ ∘ ∘ Example 65 380 0.44 ∘ x ∘ ∘ ∘ Comp. Ex. 66 408 0.45 ∘∘ ∘ ∘ ∘ Example 67 274 0.45 ∘ ∘ ∘ ∘ ∘ Example 68 508 0.50 ∘ ∘ ∘ ∘ ∘Comp. Ex. 69 387 0.52 ∘ ∘ ∘ ∘ ∘ Example 70 355 0.37 ∘ ∘ ∘ ∘ ∘ Example 71316 0.49 ∘ ∘ ∘ ∘ ∘ Example 72 346 0.48 ∘ ∘ ∘ ∘ ∘ Example 73 221 0.39 ∘ ∘∘ ∘ ∘ Example 74 288 0.48 ∘ ∘ ∘ ∘ ∘ Example 75 355 0.46 ∘ ∘ ∘ ∘ ∘Example

TABLE 38 Tensile properties Bendability Yield Maximum Total Hole Minimumstrength tensile elongation expansibility TS^(0.5) × bendingExperimental Chemical Thickness t YS strength TS El λ El × radius rExample components mm MPa MPa % % λ^(0.5) mm r/t 76 W 1.8 364 693 24 392.73E+06 1.5 0.8 77 W 1.7 335 662 25 52 3.07E+06 1.5 0.9 78 X 2.4 284556 32 61 3.28E+06 3.5 1.5 79 X 1.3 340 663 26 55 3.29E+06 2.0 1.5 80 X1.7 374 617 17 47 1.79E+06 3.0 1.8 81 Y 2.0 373 831 21 29 2.71E+06 2.51.3 82 Y 1.7 562 783 19 70 3.48E+06 3.0 1.8 83 Y 1.8 412 713 25 473.26E+06 3.0 1.7 84 Z 1.5 414 781 20 33 2.51E+06 2.0 1.3 85 Z 1.7 399758 23 36 2.88E+06 4.5 2.6 86 Z 1.7 340 682 31 27 2.87E+06 1.5 0.9 87 AA1.5 582 1137 15 18 2.44E+06 1.5 1.0 88 AA 1.9 605 908 17 42 3.01E+06 1.50.8 89 AB 1.5 578 999 17 27 2.79E+06 1.0 0.7 90 AB 1.8 401 618 31 483.30E+06 3.0 1.7 91 AB 1.7 348 583 31 52 3.15E+06 1.5 0.9 92 AC 1.3 414778 25 33 3.12E+06 1.5 1.2 93 AC 1.5 385 721 25 46 3.28E+06 2.0 1.3 94AD 1.5 527 905 20 20 2.44E+06 1.0 0.7 95 AD 1.5 537 738 23 53 3.36E+062.5 1.7 96 AE 2.0 445 785 22 41 3.10E+06 1.5 0.8 97 AE 1.9 484 709 24 613.54E+06 2.5 1.3 98 AF 1.5 398 810 24 27 2.87E+06 1.0 0.7 99 AF 1.9 6751042 18 17 2.50E+06 1.0 0.5 100 AG 1.5 536 982 18 32 3.13E+06 1.0 0.7Fatigue resistance Fatigue limit 1R90° V Experimental DL Plating SpotCorrosion Chipping bending Example MPa DL/TS adhesion weldabilityresistance Properties powdering 76 202 0.29 x ∘ ∘ ∘ ∘ Comp. Ex. 77 3010.45 ∘ ∘ ∘ ∘ ∘ Example 78 277 0.50 ∘ ∘ ∘ ∘ ∘ Example 79 299 0.45 ∘ ∘ ∘ ∘∘ Example 80 300 0.49 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 81 362 0.44 ∘ ∘ ∘ ∘ ∘ Example82 414 0.53 ∘ ∘ ∘ ∘ ∘ Example 83 375 0.53 ∘ ∘ ∘ ∘ ∘ Example 84 350 0.45∘ ∘ ∘ ∘ ∘ Example 85 209 0.28 x ∘ ∘ ∘ x Comp. Ex. 86 312 0.46 ∘ ∘ ∘ ∘ ∘Example 87 481 0.42 ∘ ∘ ∘ ∘ ∘ Example 88 474 0.52 ∘ ∘ ∘ ∘ ∘ Example 89506 0.51 ∘ ∘ ∘ ∘ ∘ Example 90 219 0.35 ∘ ∘ ∘ ∘ ∘ Example 91 298 0.51 ∘ ∘∘ ∘ ∘ Example 92 358 0.46 ∘ ∘ ∘ ∘ ∘ Example 93 303 0.42 ∘ ∘ ∘ ∘ ∘Example 94 491 0.54 ∘ ∘ ∘ ∘ ∘ Example 95 359 0.49 ∘ ∘ ∘ ∘ ∘ Example 96374 0.48 ∘ ∘ ∘ ∘ ∘ Example 97 278 0.39 ∘ ∘ ∘ ∘ ∘ Example 98 335 0.41 ∘ ∘∘ ∘ ∘ Example 99 498 0.48 ∘ ∘ ∘ ∘ ∘ Example 100 503 0.51 ∘ ∘ ∘ ∘ ∘Example

TABLE 39 Tensile properties Maximum Bendability Yield tensile Total HoleMinimum strength strength elongation expansibility TS^(0.5) × bendingExperimental Chemical Thickness t YS TS El λ El × radius r Examplecomponents mm MPa MPa % % λ^(0.5) mm r/t 101 AG 1.6 551 1012 15 282.56E+06 1.5 0.9 102 AH 0.9 621 1037 16 19 2.33E+06 1.0 1.1 103 AH 1.5482 819 20 35 2.77E+06 1.5 1.0 104 AI 1.5 448 931 18 22 2.40E+06 1.0 0.7105 AI 1.6 434 702 28 46 3.53E+06 2.5 1.6 106 AJ 1.5 475 899 20 333.10E+06 1.5 1.0 107 AJ 1.9 564 987 17 29 2.84E+06 2.5 1.3 108 AK 1.5611 1099 14 19 2.22E+06 1.5 1.0 109 AK 1.4 560 867 18 54 3.38E+06 2.01.4 110 AL 1.5 287 630 27 49 2.99E+06 2.0 1.3 111 AL 1.6 302 530 29 1153.79E+06 3.0 1.9 112 AM 1.5 598 1007 17 32 3.07E+06 1.0 0.7 113 AM 1.4632 932 18 51 3.66E+06 2.5 1.8 114 AM 1.2 636 965 17 23 2.44E+06 1.0 0.8115 AM 1.9 592 930 21 22 2.79E+06 2.5 1.3 116 AN 1.2 372 731 27 282.82E+06 1.5 1.3 117 AN 2.0 489 853 20 30 2.73E+06 1.5 0.8 118 AO 1.2381 702 23 55 3.17E+06 1.5 1.3 119 AO 1.8 465 818 20 39 2.92E+06 2.0 1.1120 AP 1.5 363 729 21 50 2.92E+06 2.0 1.3 121 AP 1.5 472 826 19 463.06E+06 1.5 1.0 122 AP 1.9 346 623 35 41 3.48E+06 2.5 1.3 123 AQ 1.5351 725 29 33 3.25E+06 1.5 1.0 124 AQ 1.4 317 595 27 52 2.83E+06 2.0 1.4125 AR 1.5 346 703 30 25 2.80E+06 2.0 1.3 Fatigue resistance Fatigue1R90° V Experimental limit DL Plating Spot Corrosion Chipping bendingExample MPa DL/TS adhesion weldability resistance Properties powdering101 460 0.45 ∘ ∘ ∘ ∘ ∘ Example 102 520 0.50 ∘ ∘ ∘ ∘ ∘ Example 103 4770.58 ∘ ∘ ∘ ∘ ∘ Example 104 360 0.39 ∘ ∘ ∘ ∘ ∘ Example 105 338 0.48 ∘ ∘ ∘∘ ∘ Example 106 423 0.47 ∘ ∘ ∘ ∘ ∘ Example 107 496 0.50 ∘ ∘ ∘ ∘ ∘Example 108 539 0.49 ∘ ∘ ∘ ∘ ∘ Example 109 391 0.45 ∘ ∘ ∘ ∘ ∘ Example110 287 0.46 ∘ ∘ ∘ ∘ ∘ Example 111 268 0.51 ∘ ∘ ∘ ∘ ∘ Example 112 5070.50 ∘ ∘ ∘ ∘ ∘ Example 113 465 0.50 ∘ ∘ ∘ ∘ ∘ Example 114 513 0.53 ∘ ∘ ∘∘ ∘ Example 115 256 0.28 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 116 367 0.50 ∘ ∘ ∘ ∘ ∘Example 117 427 0.50 ∘ ∘ ∘ ∘ ∘ Example 118 283 0.40 ∘ ∘ ∘ ∘ ∘ Example119 420 0.51 ∘ ∘ ∘ ∘ ∘ Example 120 349 0.48 ∘ ∘ ∘ ∘ ∘ Example 121 4350.53 ∘ ∘ ∘ ∘ ∘ Example 122 334 0.54 ∘ ∘ ∘ ∘ ∘ Example 123 287 0.40 ∘ ∘ ∘∘ ∘ Example 124 298 0.50 ∘ ∘ ∘ ∘ ∘ Example 125 321 0.46 ∘ ∘ ∘ ∘ ∘Example

TABLE 40 Tensile properties Bendability Yield Maximum Total Hole Minimumstrength tensile elongation expansibility TS^(0.5) × bendingExperimental Chemical Thickness t YS strength TS El λ El × radius rExample components mm MPa MPa % % λ^(0.5) mm r/t 126 AR 1.8 381 718 2437 2.81E+06 3.0 1.7 127 AS 2.1 434 848 23 24 2.78E+06 2.5 1.2 128 AS 1.5539 843 21 40 3.25E+06 2.0 1.3 129 AT 1.5 389 825 21 27 2.59E+06 1.0 0.7130 AT 1.2 310 637 33 43 3.48E+06 2.0 1.7 131 AU 1.5 416 904 20 222.55E+06 1.5 1.0 132 AU 2.0 437 842 22 21 2.46E+06 5.0 2.5 133 AU 2.0369 756 23 37 2.91E+06 1.5 0.8 134 AU 1.9 343 747 22 41 2.88E+06 2.0 1.1135 AV 0.9 481 932 17 42 3.13E+06 1.0 1.1 136 AV 2.0 558 941 19 333.15E+06 2.5 1.3 137 AV 1.3 557 901 18 39 3.04E+06 1.5 1.2 138 AW 0.9433 831 22 30 2.89E+06 1.0 1.1 139 AW 1.4 355 543 21 39 1.66E+06 2.5 1.8140 AW 1.7 400 637 27 60 3.36E+06 1.5 0.9 141 AX 1.5 502 899 19 242.51E+06 2.0 1.3 142 AX 1.8 395 746 25 37 3.10E+06 2.0 1.1 143 AY 1.5616 1098 15 23 2.62E+06 1.5 1.0 144 AY 2.0 465 722 27 28 2.77E+06 3.51.8 145 AZ 0.9 396 744 21 59 3.27E+06 1.5 1.7 146 AZ 1.2 395 709 27 383.14E+06 1.5 1.3 147 BA 1.5 465 842 23 28 2.97E+06 2.0 1.3 148 BA 1.6542 883 19 30 2.73E+06 2.0 1.3 149 BB 1.5 625 995 19 22 2.80E+06 1.5 1.0150 BB 1.5 458 866 20 23 2.44E+06 3.5 2.3 Fatigue resistance Fatigue1R90° V Experimental limit DL Plating Spot Corrosion Chipping bendingExample MPa DL/TS adhesion weldability resistance Properties powdering126 353 0.49 ∘ ∘ ∘ ∘ ∘ Example 127 361 0.43 ∘ ∘ ∘ ∘ ∘ Example 128 3540.42 ∘ ∘ ∘ ∘ ∘ Example 129 359 0.44 ∘ ∘ ∘ ∘ ∘ Example 130 298 0.47 ∘ ∘ ∘∘ ∘ Example 131 404 0.45 ∘ ∘ ∘ ∘ ∘ Example 132 381 0.45 ∘ ∘ ∘ ∘ ∘ Comp.Ex. 133 348 0.46 ∘ ∘ ∘ ∘ ∘ Example 134 333 0.45 ∘ ∘ ∘ ∘ ∘ Example 135416 0.45 ∘ ∘ ∘ ∘ ∘ Example 136 392 0.42 ∘ ∘ x Unmeasurable Comp. Ex. 137425 0.47 ∘ ∘ ∘ ∘ ∘ Example 138 374 0.45 ∘ ∘ ∘ ∘ ∘ Example 139 224 0.41 ∘∘ ∘ ∘ ∘ Comp. Ex. 140 309 0.49 ∘ ∘ ∘ ∘ ∘ Example 141 433 0.48 ∘ ∘ ∘ ∘ ∘Example 142 329 0.44 ∘ ∘ ∘ ∘ ∘ Example 143 473 0.43 ∘ ∘ ∘ ∘ ∘ Example144 408 0.57 ∘ ∘ ∘ ∘ ∘ Example 145 388 0.52 ∘ ∘ ∘ ∘ ∘ Example 146 3420.48 ∘ ∘ ∘ ∘ ∘ Example 147 415 0.49 ∘ ∘ ∘ ∘ ∘ Example 148 487 0.55 ∘ ∘ ∘∘ ∘ Example 149 537 0.54 ∘ ∘ ∘ ∘ ∘ Example 150 445 0.51 x ∘ ∘ ∘ ∘ Comp.Ex.

TABLE 41 Tensile properties Bendability Yield Maximum Total Hole Minimumstrength tensile elongation expansibility TS^(0.5) × bendingExperimental Chemical Thickness t YS strength TS El λ El × radius rExample components mm MPa MPa % % λ^(0.5) mm r/t 151 BB 2.2 492 761 2242 2.99E+06 3.0 1.4 152 BB 2.0 542 854 22 35 3.25E+06 2.0 1.0 153 BC 1.1271 598 29 58 3.23E+06 1.5 1.4 154 BC 1.3 427 687 24 46 2.93E+06 1.5 1.2155 BC 1.7 443 762 23 45 3.25E+06 1.5 0.9 156 BC 2.0 330 594 29 613.28E+06 2.5 1.3 157 BC 1.2 361 686 27 35 2.87E+06 3.0 2.5 158 BD 1.5353 706 29 24 2.67E+06 1.0 0.7 159 BD 1.7 369 696 26 45 3.20E+06 1.5 0.9160 BE 1.5 421 753 26 28 2.84E+06 1.0 0.7 161 BE 1.9 384 742 25 363.03E+06 2.5 1.3 162 BF 1.0 480 879 20 35 3.08E+06 1.5 1.5 163 BF 1.7568 1055 14 38 2.96E+06 1.5 0.9 164 BF 1.5 567 899 20 26 2.75E+06 1.51.0 165 BF 0.9 534 899 26 37 4.26E+06 2.0 2.2 166 BG 1.0 353 686 27 342.83E+06 1.0 1.0 167 BG 1.5 792 940 19 46 3.71E+06 2.5 1.7 168 BG 1.5348 690 25 48 3.14E+06 3.0 2.0 169 BG 1.2 419 776 24 33 2.98E+06 1.5 1.3170 BH 1.2 513 911 17 30 2.56E+06 1.0 0.7 171 BH 1.9 590 1052 15 242.51E+06 1.0 0.5 172 BH 1.8 583 861 22 27 2.89E+06 1.0 0.6 173 BH 1.3513 818 20 47 3.21E+06 1.5 1.2 174 BI 1.5 345 675 28 44 3.26E+06 2.0 1.3175 BI 1.2 296 481 41 43 2.84E+06 2.0 1.7 Fatigue resistance Fatigue1R90° V Experimental limit DL Plating Spot Corrosion Chipping bendingExample MPa DL/TS adhesion weldability resistance Properties powdering151 369 0.48 ∘ ∘ ∘ ∘ ∘ Example 152 458 0.54 ∘ ∘ ∘ ∘ ∘ Example 153 2830.47 ∘ ∘ ∘ ∘ ∘ Example 154 385 0.56 ∘ ∘ ∘ ∘ ∘ Example 155 384 0.50 ∘ ∘ ∘∘ ∘ Example 156 310 0.52 ∘ ∘ ∘ ∘ ∘ Example 157 381 0.56 ∘ ∘ ∘ ∘ ∘ Comp.Ex. 158 293 0.42 ∘ ∘ ∘ ∘ ∘ Example 159 362 0.52 ∘ ∘ ∘ ∘ ∘ Example 160359 0.48 ∘ ∘ ∘ ∘ ∘ Example 161 329 0.44 ∘ ∘ ∘ ∘ ∘ Example 162 376 0.43 ∘∘ ∘ ∘ ∘ Example 163 495 0.47 ∘ ∘ ∘ ∘ ∘ Example 164 460 0.51 ∘ ∘ ∘ ∘ ∘Example 165 419 0.47 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 166 295 0.43 ∘ ∘ ∘ ∘ ∘ Example167 615 0.65 ∘ ∘ ∘ ∘ ∘ Example 168 197 0.29 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 169 3540.46 ∘ ∘ ∘ ∘ ∘ Example 170 457 0.50 ∘ ∘ ∘ ∘ ∘ Example 171 535 0.51 x ∘ ∘∘ ∘ Comp. Ex. 172 475 0.55 ∘ ∘ ∘ ∘ ∘ Example 173 488 0.60 ∘ ∘ ∘ ∘ ∘Example 174 317 0.47 ∘ ∘ ∘ ∘ ∘ Example 175 215 0.45 ∘ ∘ ∘ ∘ ∘ Example

TABLE 42 Tensile properties Bendability Yield Maximum Total Hole Minimumstrength tensile elongation expansibility TS^(0.5) × bendingExperimental Chemical Thickness t YS strength TS El λ El × radius rExample components mm MPa MPa % % λ^(0.5) mm r/t 176 BJ 1.5 416 858 1756 3.20E+06 1.5 1.0 177 BJ 1.4 386 630 19 25 1.50E+06 2.5 1.8 178 BJ 1.5450 972 17 28 2.73E+06 2.0 1.3 179 BK 1.3 307 671 30 29 2.81E+06 2.0 1.5180 BL 1.3 378 684 24 45 2.88E+06 2.0 1.5 181 BL 1.3 357 718 26 373.04E+06 1.5 1.2 182 BL 2.0 447 692 28 50 3.60E+06 3.5 1.8 183 BL 1.9379 740 24 34 2.82E+06 1.5 0.8 184 BL 1.3 375 635 30 54 3.53E+06 2.6 2.0185 BM 1.5 486 921 17 33 2.73E+06 1.0 0.7 186 BM 1.4 261 551 21 311.51E+06 2.5 1.8 187 BM 1.6 482 885 20 34 3.07E+06 2.0 1.3 188 BN 1.5354 706 24 44 2.99E+06 2.0 1.3 189 BN 1.2 385 641 29 56 3.52E+06 2.0 1.7190 BO 1.5 160 365 37 52 1.86E+06 1.0 0.7 191 BP 1.5 870 1460  5 131.01E+06 5.5 3.7 192 BQ 1.5 292 462 27 29 1.44E+06 4.0 2.7 193 BRExperiment stopped due to occurrence of cracking of slab during heatingin hot rolling step 194 BS 1.5 230 430 30 35 1.58E+06 3.5 2.3 195 BTExperiment stopped due to occurrence of cracking of slab during heatingin hot rolling step 196 BU Experiment stopped due to occurrence ofcracking of slab during hot rolling in hot rolling step 197 BV 1.5 485830 13 16 1.24E+06 5.0 3.3 198 BW Experiment stopped due to occurrenceof cracking of slab during transportation after casting of slab 199 BX1.5 442 756 14 12 1.01E+06 5.0 3.3 200 BY 1.5 635 1204 3 5 2.80E+05 over6.0 over 4.0 201 A 1.5 452 745 24 38 2.99E+06 1.5 1.0 Fatigue resistanceFatigue 1R90° V Experimental limit DL Plating Spot Corrosion Chippingbending Example MPa DL/TS adhesion weldability resistance Propertiespowdering 176 412 0.48 ∘ ∘ ∘ ∘ ∘ Example 177 349 0.55 ∘ ∘ ∘ ∘ ∘ Comp.Ex. 178 433 0.45 ∘ ∘ ∘ ∘ ∘ Example 179 282 0.42 ∘ ∘ ∘ ∘ ∘ Example 180346 0.51 ∘ ∘ ∘ ∘ ∘ Example 181 338 0.47 ∘ ∘ ∘ ∘ ∘ Example 182 431 0.62 ∘∘ ∘ ∘ ∘ Example 183 361 0.49 x ∘ ∘ x x Comp. Ex. 184 353 0.56 ∘ ∘ ∘ ∘ ∘Example 185 397 0.43 ∘ ∘ ∘ ∘ ∘ Example 186 216 0.39 ∘ ∘ ∘ ∘ ∘ Comp. Ex.187 418 0.47 ∘ ∘ ∘ ∘ ∘ Example 188 314 0.44 ∘ ∘ ∘ ∘ ∘ Example 189 3680.57 ∘ ∘ ∘ ∘ ∘ Example 190 155 0.42 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 191 423 0.29 ∘ x∘ ∘ ∘ Comp. Ex. 192 175 0.38 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 193 Experiment stoppeddue to occurrence of cracking of Comp. Ex. slab during heating in hotrolling step 194 155 0.36 ∘ ∘ ∘ ∘ ∘ Comp. Ex. 195 Experiment stopped dueto occurrence of cracking Comp. Ex. of slab during heating in hotrolling step 196 Experiment stopped due to occurrence of cracking Comp.Ex. of slab during hot rolling in hot rolling step 197 234 0.28 ∘ x ∘ ∘∘ Comp. Ex. 198 Experiment stopped due to occurrence of cracking ofComp. Ex. slab during transportation after casting of slab 199 208 0.28∘ x ∘ ∘ ∘ Comp. Ex. 200 298 0.25 ∘ x ∘ ∘ ∘ Comp. Ex. 201 380 0.51 x ∘ ∘∘ ∘ Comp. Ex.

Experimental Example 190 is an example in which since the C content waslow and the volume fraction of the hard phase was low, sufficientstrength, ductility and hole expansibility could not be obtained.

Experimental Example 191 is an example in which the C content was highand spot weldability deteriorated. Further, a fraction of martensite washigh, and fatigue resistance, ductility hole expansibility andbendability were deteriorated.

Experimental Example 192 is an example in which since the Si content waslow, large amounts of pearlite and coarse cementite were formed in theannealing step and the plating step, formability of the steel sheetcould not be sufficiently obtained.

Experimental Example 193 is an example in which the experiment wasstopped since the Si content was high and the slab was cracked duringheating in the hot rolling step.

Experimental Example 194 is an example in which since the Mn content waslow, large amounts of pearlite and coarse cementite were formed in theannealing step and the plating step, formability of the steel sheetcould not be sufficiently obtained.

Experimental Example 195 is an example in which the experiment wasstopped since the Mn content was high and the slab was cracked duringheating in the hot rolling step.

Experimental Example 196 is an example in which the experiment wasstopped since the P content was high and the slab was cracked afterrolling in the hot rolling step.

Experimental Example 197 is an example in which since the S content washigh and a large amount of coarse sulfides were formed, ductility, holeexpansibility, bendability, spot weldability and fatigue resistancedeteriorated.

Experimental Example 198 is an example in which the experiment wasstopped since the Al content was high and the slab was cracked duringtransportation in the hot rolling step.

Experimental Example 199 is an example in which since the N content washigh and a large amount of coarse nitrides were formed, ductility, holeexpansibility, bendability, spot weldability and fatigue resistancedeteriorated.

Experimental Example 200 is an example in which since the O content washigh and a large amount of coarse oxides were formed, ductility, holeexpansibility, bendability, spot weldability and fatigue resistancedeteriorated.

Experimental Examples 27, 132, and 157 are examples in which since thevalue of Expression (1) was small in the hot rolling step, the fraction(V1/V2) of the hard phase in the surface layer became high, andsufficient bendability could not be obtained.

Experimental Examples 51, 115, and 168 are examples in which since thevalue of Expression (1) was large in the hot rolling step,decarburization excessively proceeded in the surface layer and thefraction (V1/V2) of the hard phase became small, and sufficient fatigueresistance could not be obtained.

Experimental Example 85 is an example in which since the average heatingrate at 600° C. to 750° C. was too small, growth of oxidationexcessively proceeded inside the steel sheet and coarse oxides which actas a fracture origin were formed, bendability and fatigue resistancedeteriorated. With a deterioration of bendability, in an evaluation testof plating adhesion and powdering property, plating peeling originatingfrom bending and cracking of the steel sheet occurred, and thereforeplating adhesion and powdering property deteriorated.

Experimental Example 68 is an example in which since the maximum heatingtemperature (T_(M)) was more than Ac3 point in the annealing step, andthe volume fraction of the ferrite phase at the ¼ thickness was low,ductility and bendability deteriorated.

Experimental Example 186 is an example in which since the maximumheating temperature (T_(M)) was less than (Ac1 point+20°)° C. in theannealing step, and the coarse iron-based carbides remained withoutmelting, ductility and hole expansibility deteriorated.

Experimental Example 46 is an example in which since the air ratio inthe preheating zone was small in the heating step of the annealing step,plating adhesion deteriorated. Since plating peeling occurred at thetime of bending deformation by the deterioration of plating adhesion,bendability also deteriorated.

Experimental Example 14 is an example in which since the air ratio inthe preheating zone was large in the heating step of the annealing step,decarburization excessively proceeded in the surface layer and thefraction (V1/V2) of the hard phase became small, fatigue resistancedeteriorated.

Experimental Example 171 is an example in which since the ratio betweenthe water vapor partial pressure P(H₂O) and the hydrogen partialpressure P(H₂), P(H₂O)/P(H₂), in the reduction zone in the heating stepof the annealing step was small, the grain size of the surface of thebase steel sheet was not refined, and ζ phase formation did not proceedin the plated layer, plating adhesion was deteriorated. Here, therefined layer was not formed, the average grain size of the ferrite inthe surface of the base steel sheet was 3.4 μm, and the maximum size ofthe oxides was less than 0.01 μm inside the steel sheet within a rangeup to 0.5 μm from the surface.

Experimental Example 201 is an example in which since the ratio betweenthe water vapor partial pressure P(H₂O) and the hydrogen partialpressure P(H₂), P(H₂O)/P(H₂), in the reduction zone in the heating stepof the annealing step was large, the refined layer of the surface of thebase steel sheet was excessively thick, and alloying of the plated layerexcessively proceeded, plating adhesion deteriorated.

Experimental Example 76 is an example in which since the ratio betweenthe water vapor partial pressure P(H₂O) and the hydrogen partialpressure P(H₂), P(H₂O)/P(H₂), in the reduction zone in the heating stepof the annealing step was specifically large, decarburizationexcessively proceeded in the surface layer and the fraction (V1/V2) ofthe hard phase became small, and fatigue resistance deteriorated.

Experimental Example 20 is an example in which since the average coolingrate (average cooling rate 1) between 760° C. and 700° C. was low in thecooling step of the annealing step, a large amount of pearlite wasformed, ductility and hole expansibility deteriorated.

Experimental Example 49 is an example in which since the average coolingrate (average cooling rate 1) between 760° C. and 700° C. was high inthe cooling step of the annealing step, and the volume fraction of theferrite phase at the ¼ thickness was low, sufficient ductility could notbe obtained.

Experimental Example 139 is an example in which since the averagecooling rate (average cooling rate 2) between 650° C. and 500° C. waslow in the cooling step of the annealing step, a large amount ofpearlite was formed, ductility and hole expansibility deteriorated.

Experimental Example 2 is an example in which the amount of effective Alin the plating bath was small and the amount of Fe in the plated layerwas large in the plating step, plating adhesion deteriorated.

Experimental Example 150 is an example in which the amount of effectiveAl in the plating bath and Al in the plated layer increased and theratio of the interface between the ζ phase, and the base steel in theentire interface between the plated layer and the base steel,bendability and plating adhesion deteriorated.

Experimental Example 12 is an example in which since the value ofExpression (2) was small in the plating step and the ratio of theinterface between the r phase and the base steel in the entire interfacebetween the plated layer and the base steel, plating adhesiondeteriorated.

Experimental Example 183 is an example in which since the value ofExpression (2) was large in the plating step and the amount of Fe in theplated layer was large in the plating step, plating adhesiondeteriorated.

Experimental Example 65 is an example in which since the blowingpressure of the mixed gas mainly including nitrogen after the immersionwas low in the plating bath in the plating step, and the plated amountof the plating layer excessively increased, spot weldabilitydeteriorated.

Experimental Example 136 is an example in which since the blowingpressure of the mixed gas mainly including nitrogen after the immersionwas high in the plating bath in the plating step, and the plated amountof the plating layer decreased, and sufficient corrosion resistancecould not be obtained.

Experimental Examples 7, 15, 30, 42, 82, and 182 are examples in whichthe martensitic transformation treatment was applied in the cooling stepof the annealing step, and high strength hot-dip galvanized steel sheetsexcellent in formability, plating adhesion, weldability, corrosionresistance and fatigue resistance were obtained.

Experimental Examples 3, 36, 45, 67, 90, 103, 105, 109, 144, 151, 164,and 184 are examples in which the bainitic transformation treatment 1was applied in the cooling step of the annealing step, and high strengthhot-dip galvanized steel sheets excellent in formability, platingadhesion, weldability, corrosion resistance and fatigue resistance wereobtained.

Experimental Example 43 is an example in which the bainitictransformation treatment 1 was applied in the cooling step of theannealing step. However, since the treatment temperature was high,pearlite and coarse cementite were formed, ductility and holeexpansibility deteriorated.

Experimental Example 177 is an example in which the bainitictransformation treatment 1 was applied in the cooling step of theannealing step. However, since the treatment time was long, pearlite andcoarse cementite were formed, and ductility and hole expansibilitydeteriorated.

Experimental Examples 23, 40, 55, 91, 114, 137, 154, 173, and 187 areexamples in which the bainitic transformation treatment 2 was applied inthe cooling step after the plating step, and high strength hot-dipgalvanized steel sheets excellent in formability, plating adhesion,weldability, corrosion resistance and fatigue resistance were obtained.

Experimental Example 165 is an example in which the bainitictransformation treatment 2 was applied in the cooling step after theplating step. However, since the treatment temperature was high, a largeamount of residual austenite was formed, bendability deteriorated.

Experimental Examples 4, 18, 26, 48, 53, 62, 74, 77, 88, 95, 113, 130,167, and 189 are examples in which the reheating treatment was appliedin the cooling step after the plating step, and high strength hot-dipgalvanized steel sheets excellent in formability, plating adhesion,weldability, corrosion resistance and fatigue resistance were obtained.

Experimental Example 16 is an example in which the martensitictransformation treatment and the bainitic transformation treatment 1were applied in the cooling step of the annealing step, and highstrength hot-dip galvanized steel sheets excellent in formability,plating adhesion, weldability, corrosion resistance and fatigueresistance were obtained.

Experimental Examples 8, 111, 133, 140, 156, and 172 are examples inwhich the bainitic transformation treatment 1 was applied in the coolingstep of the annealing step, and then the bainitic transformationtreatment 2 was applied in the cooling step after the plating step, andhigh strength hot-dip galvanized steel sheets excellent in formability,plating adhesion, weldability, corrosion resistance and fatigueresistance were obtained.

Experimental Examples 22, 33, and 97 are examples in which the bainitictransformation treatment 1 was applied in the cooling step of theannealing step, and then the reheating treatment was applied in thecooling step after the plating step, and high strength hot-dipgalvanized steel sheets excellent in formability, plating adhesion,weldability, corrosion resistance and fatigue resistance were obtained.

Experimental Example 10 is an example in which the bainitictransformation treatment 2 and the reheating treatment were applied inthe cooling step after the plating step, and high strength hot-dipgalvanized steel sheets excellent in formability, plating adhesion,weldability, corrosion resistance and fatigue resistance were obtained.

Experimental Example 175 is an example in which the bainitictransformation treatment 1 was applied in the cooling step of theannealing step, and then the bainitic transformation treatment 2 and thereheating treatment were applied in the cooling step after the platingstep, and high strength hot-dip galvanized steel sheets excellent informability, plating adhesion, weldability, corrosion resistance andfatigue resistance were obtained.

Experimental Example 80 is an example in which since a diameter of aroll used for the processing was small and excessive strain wasintroduced in the surface layer of the base steel sheet in thebending-bending back processing step of the processing step, ductilitydeteriorated.

Experimental Example 59 is an example in which since a diameter of aroll used for the processing was large and sufficient strain was notintroduced in the surface layer of the base steel sheet in thebending-bending back processing step of the processing step, and a largeamount of residual austenite presented in the surface layer of the basesteel sheet, bendability deteriorated.

Although each embodiment and experimental examples of the presentinvention has been described in detail above, all of these embodimentsand these experimental examples are merely examples of embodiments inimplementation of the present invention. The technical scope of thepresent invention should not be interpreted as limited only by theembodiments. That is, the present invention can be implemented invarious forms without departing from the technical idea thereof or themain features thereof.

INDUSTRIAL APPLICABILITY

The present invention is an effective technology for a high strengthhot-dip galvanized steel sheet excellent in formability, fatigueresistance, weldability, corrosion resistance, and plating adhesion andproduction method thereof. According to the embodiment of the presentinvention, it is possible to provide a high strength hot-dip galvanizedsteel sheet excellent in ductility, hole expansibility and bendabilityand further excellent in plating adhesion after forming, having highfatigue limit, and having excellent spot weldability and corrosionresistance, and production method thereof.

The invention claimed is:
 1. A hot-dip galvanized steel sheetcomprising: a base steel sheet; and a hot-dip galvanized layer formed onat least one surface of the base steel sheet, wherein: the base steelsheet includes, a chemical composition comprising, % by mass, C: 0.040%to 0.280%, Si: 0.05% to 2.00%, Mn: 0.50% to 3.50%, P: 0.0001% to0.1000%, S: 0.0001% to 0.0100%, Al: 0.001% to 1.500%, N: 0.0001% to0.0100%, O: 0.0001% to 0.0100%, and a remainder of Fe and impurities; ina range of ⅛ thickness to ⅜ thickness centered at a position of ¼thickness from the surface of the base steel sheet, by volume fraction,40% or more and 97% or less of a ferrite phase, a total of 3% by volumefraction or more of a hard structure comprising one or more of a bainitephase, a bainitic ferrite phase, a fresh martensite phase and a temperedmartensite phase, a residual austenite phase is 0 to 8% by volumefraction, a total of a pearlite phase and a coarse cementite phase is 0to 8% by volume fraction, in a surface layer range of 20 μm depth in asteel sheet direction from an interface between the hot-dip galvanizedlayer and the base steel sheet, a volume fraction of a residualaustenite is 0 to 3%, the base steel sheet includes a microstructure inwhich V1/V2 which is a ratio of a volume fraction V1 of the hardstructure in the surface layer range and a volume fraction V2 of thehard structure in the range of ⅛ thickness to ⅜ thickness centered atthe position of ¼ thickness from the surface of the base steel sheet is0.10 or more and 0.90 or less, a Fe content is more than 0% by mass to5.0% by mass or less and an Al content is more than 0% by mass to 1.0%by mass or less in the hot-dip galvanized layer, and columnar grainsformed of a ζ phase are included in the hot-dip galvanized layer, aratio ((A*/A)×100) of an interface (A*) between the ζ phase and the basesteel sheet in an entire interface (A) between the hot-dip galvanizedplated layer and the base steel sheet is 20% or more, a refined layer isformed at the side of the interface in the base steel sheet, an averagethickness of the refined layer is 0.1 to 5.0 μm, an average grain sizeof ferrite in the refined layer is 0.1 to 3.0 μm, one or two or more ofoxides of Si and Mn are contained, and a maximum size of the oxide is0.01 to 0.4 μm.
 2. The hot-dip galvanized steel sheet according to claim1, wherein the base steel sheet further contains, % by mass, one or twoor more selected from Ti: 0.001% to 0.150%, Nb: 0.001% to 0.100%, and V:0.001% to 0.300%.
 3. The hot-dip galvanized steel sheet according toclaim 1, wherein the base steel sheet contains, % by mass, one or two ormore selected from Cr: 0.01% to 2.00%, Ni: 0.01% to 2.00%, Cu: 0.01% to2.00%, Mo: 0.01% to 2.00%, B: 0.0001% to 0.0100%, and W: 0.01% to 2.00%.4. The hot-dip galvanized steel sheet according to claim 2, wherein thebase steel sheet contains, % by mass, one or two or more selected fromCr: 0.01% to 2.00%, Ni: 0.01% to 2.00%, Cu: 0.01% to 2.00%, Mo: 0.01% to2.00%, B: 0.0001% to 0.0100%, and W: 0.01% to 2.00%.
 5. The hot-dipgalvanized steel sheet according to claim 1, wherein the base steelsheet contains, % by mass, one or two or more selected from Ca, Ce, Mg,Zr, La, and REM in a total amount of 0.0001% to 0.0100%.
 6. The hot-dipgalvanized steel sheet according to claim 2, wherein the base steelsheet contains, % by mass, one or two or more selected from Ca, Ce, Mg,Zr, La, and REM in a total amount of 0.0001% to 0.0100%.
 7. The hot-dipgalvanized steel sheet according to claim 3, wherein the base steelsheet contains, % by mass, one or two or more selected from Ca, Ce, Mg,Zr, La, and REM in a total amount of 0.0001% to 0.0100%.
 8. The hot-dipgalvanized steel sheet according to claim 4, wherein the base steelsheet contains, % by mass, one or two or more selected from Ca, Ce, Mg,Zr, La, and REM in a total amount of 0.0001% to 0.0100%.
 9. The hot-dipgalvanized steel sheet according to claim 1, wherein a ratio((A**/A*)×100) of an interface (A**) formed between ζ grains in whichcoarse oxides are present and the base steel sheet in an interface (A*)between the ζ phase and the base steel sheet in the hot-dip galvanizedlayer is 50% or less.
 10. The hot-dip galvanized steel sheet accordingto claim 2, wherein a ratio ((A**/A*)×100) of an interface (A**) formedbetween ζ grains in which coarse oxides are present and the base steelsheet in an interface (A*) between the ζ phase and the base steel sheetin the hot-dip galvanized layer is 50% or less.
 11. The hot-dipgalvanized steel sheet according to claim 3, wherein a ratio((A**/A*)×100) of an interface (A**) formed between ζ grains in whichcoarse oxides are present and the base steel sheet in an interface (A*)between the ζ phase and the base steel sheet in the hot-dip galvanizedlayer is 50% or less.
 12. The hot-dip galvanized steel sheet accordingto claim 4, wherein a ratio ((A**/A*)×100) of an interface (A**) formedbetween ζ grains in which coarse oxides are present and the base steelsheet in an interface (A*) between the ζ phase and the base steel sheetin the hot-dip galvanized layer is 50% or less.
 13. The hot-dipgalvanized steel sheet according to claim 5, wherein a ratio((A**/A*)×100) of an interface (A**) formed between ζ grains in whichcoarse oxides are present and the base steel sheet in an interface (A*)between the ζ phase and the base steel sheet in the hot-dip galvanizedlayer is 50% or less.
 14. The hot-dip galvanized steel sheet accordingto claim 6, wherein a ratio ((A**/A*)×100) of an interface (A**) formedbetween ζ grains in which coarse oxides are present and the base steelsheet in an interface (A*) between the ζ phase and the base steel sheetin the hot-dip galvanized layer is 50% or less.
 15. The hot-dipgalvanized steel sheet according to claim 7, wherein a ratio((A**/A*)×100) of an interface (A**) formed between ζ grains in whichcoarse oxides are present and the base steel sheet in an interface (A*)between the ζ phase and the base steel sheet in the hot-dip galvanizedlayer is 50% or less.
 16. The hot-dip galvanized steel sheet accordingto claim 8, wherein a ratio ((A**/A*)×100) of an interface (A**) formedbetween ζ grains in which coarse oxides are present and the base steelsheet in an interface (A*) between the ζ phase and the base steel sheetin the hot-dip galvanized layer is 50% or less.
 17. The hot-dipgalvanized steel sheet according to claim 1, wherein a plated amount onone surface of the base steel sheet in the hot-dip galvanized layer is10 g/m² or more and 100 g/m² or less.
 18. The hot-dip galvanized steelsheet according to claim 2, wherein a plated amount on one surface ofthe base steel sheet in the hot-dip galvanized layer is 10 g/m² or moreand 100 g/m² or less.
 19. The hot-dip galvanized steel sheet accordingto claim 3, wherein a plated amount on one surface of the base steelsheet in the hot-dip galvanized layer is 10 g/m² or more and 100 g/m² orless.
 20. The hot-dip galvanized steel sheet according to claim 4,wherein a plated amount on one surface of the base steel sheet in thehot-dip galvanized layer is 10 g/m² or more and 100 g/m² or less.